Added a new calculator, True Dip from Apparent Dip (Geology > Structural), that solves the same true-dip/apparent-dip relationship used by the existing Apparent Dip from True Dip calculator in the opposite direction: enter a dip you've actually observed in an outcrop, road cut, or seismic section (an apparent dip) along with that section's angle from strike, and recover the plane's true dip. This is generally the more useful direction in the field, since apparent dip is what you can directly see and true dip is what you usually need for mapping or volumetrics. The two calculators are cross-linked under Related Calculations.

QFL Sandstone Classification (Geology > Petrology) now draws its result as an actual ternary diagram — the classic triangular Q/F/L plot geologists use to classify sandstone composition — rather than just the classification table it shipped with. Each pasted sample is plotted as a point inside the triangle, positioned by its own quartz/feldspar/lithic-fragment percentages, against the seven named Folk (1968) composition fields (Quartzarenite, Subarkose, Sublitharenite, Arkose, Lithic Arkose, Litharenite, Feldspathic Litharenite) drawn directly on the chart as labeled regions, so you can see at a glance which field a sample falls in rather than reading it only from the table. This is the first three-sided (ternary) chart on this site — every other chart here plots a value against one or two straight axes — so it's built as its own new chart type rather than a variation on the existing chart engine. Closes out the QFL Ternary Diagram as a complete feature; a provenance-diagram variant (which uses different, less standardized boundaries) and multi-sample display refinements remain deliberately out of scope for now.

Added two more sections to the Constants & Standard Values reference page. The first, Porosity by Rock Type, gives typical porosity ranges for unconsolidated sand, sandstone, limestone, dolomite, shale, and chalk — clearly marked as typical defaults rather than universal values, since real porosity overlaps heavily across rock types depending on how deeply buried, cemented, or altered a given rock has been. The second, Depositional Environments, is a simple reference list of the eight standard settings sedimentary rocks form in — river (fluvial), delta, shoreface, shelf, deep marine/turbidite, wind-blown (eolian), lake (lacustrine), and glacial — each with a one-line description and a note on how that setting typically behaves as an oil and gas reservoir target. This closes out the six-part static reference series that also added the grain-size scale, carbonate rock classification, stratigraphic column symbols, and the geologic time scale over the past several sessions.

Added a Geologic Time Scale to the Constants & Standard Values reference page — the International Chronostratigraphic Chart, organized Eon > Era > Period > Epoch, from the Holocene back through the Precambrian, with each unit's numeric age boundary in millions of years. Unlike everything else on that page, this one is explicitly not a "set it and forget it" reference: the chart's numeric ages get revised by the International Commission on Stratigraphy every so often as dating methods improve, so the exact version used and the date it was last checked are both shown directly on the page, next to the citation, along with a link to the ICS's own site to check for anything newer. Two of the ages shown (Middle Triassic and the base of the Permian's Lopingian epoch) changed in the chart's most recent revision and are marked with a small asterisk noting the prior value. Precambrian time — essentially never a subsurface target for this site's purposes — is shown at a coarser level of detail than the more geologically-recent Phanerozoic eon, to keep the table a reasonable size.

Added a Stratigraphic Column Lithology Symbols legend to the Constants & Standard Values reference page, showing the standard area-fill pattern used to represent 7 common lithologies (sandstone, shale, limestone, dolomite, coal, anhydrite/evaporite, and conglomerate) on a stratigraphic column, cross-section, or geologic map — per the FGDC's official Digital Cartographic Standard for Geologic Map Symbolization (FGDC-STD-013-2006). Each swatch reproduces that pattern's defining visual device (a dot scatter for sandstone, short dashes for shale, offset brick coursing for limestone and dolomite, a diagonal cross-hatch for evaporite, a solid fill for coal, and larger scattered circles for conglomerate) rather than the standard's literal printed line art, which is drawn for large-format map sheets and isn't legible at legend size. Worth noting for anyone cross-checking against the standard directly: several of these lithologies have multiple pattern variants (different bedding styles for sandstone, different compositions for shale/limestone/dolomite) — the plainest, most generic variant was used for each; and the standard has no distinct "anhydrite" pattern at all, so its Gypsum pattern is used here as a disclosed stand-in for that category.

Added three new sections to the Constants & Standard Values reference page, all about how sedimentary rocks are classified. A new "Sedimentary Rock Classification" overview sits at the top, giving a quick map of the four broad families (siliciclastic rocks like sandstone and shale, carbonates like limestone and dolomite, chemical/evaporite rocks like rock salt and chert, and organic rocks like coal) before diving into detail on one of them. Directly below it are two different, still both actively used, ways geologists classify carbonate rocks specifically: Dunham's (1962) scheme, which sorts a carbonate rock by its depositional texture — how much mud it has, whether its grains support each other, and whether it shows signs of having been bound together as it formed (mudstone, wackestone, packstone, grainstone, boundstone, and crystalline) — and Folk's (1959, 1962) scheme, a more detailed petrographic system built around the proportion of grains, mud matrix, and sparry cement a carbonate rock contains, presented here as an eight-step spectrum from pure mud to pure cement. These are presented side by side as two genuinely different tools for two different jobs, not an old one and a new one — Dunham for a quick reservoir-fabric read, Folk for finer petrographic/diagenetic detail — since both remain standard practice today. As with the Udden-Wentworth scale added earlier, none of this is a typical default to calibrate; these are fixed classification standards.

Added the Udden-Wentworth grain-size classification scale to the Constants & Standard Values reference page — a standard geology table (boulder, cobble, pebble, and granule down through five grades of sand to silt and clay) showing each grade's size range in both millimeters and the phi (Φ) scale geologists commonly use instead. Unlike this page's other entries, which are explicitly typical defaults rather than universal values, this classification has been essentially unchanged and universally adopted since it was first published in 1922, so it's presented as a fixed reference standard rather than a correlation to calibrate. This closes out this site's chart-visualization work for now — the last item in a longer-running series of additions (Ricker Wavelet, Horner Plot, Well Trajectory Profile, Mud-Window Plot, and others above) that started from a single early brainstorm.

Ricker Wavelet's chart now also marks two different bed-thickness resolution estimates directly on the wavelet shape, closing out the follow-up promised when this calculator first shipped. The classic Widess (1973) quarter-wavelength rule of thumb — the same one behind Vertical Resolution (Tuning Thickness) elsewhere in this section — is marked as one line; a more precise estimate from Chung & Lawton (1995), which works out to noticeably less than a quarter wavelength for this specific wavelet shape, is marked as a second, distinctly colored line. Both are labeled plainly as two different answers to two related but different questions, not one correcting the other, and two new result fields report both bed thicknesses directly in feet or meters. Also corrected a citation mix-up in the existing Vertical Resolution (Tuning Thickness) calculator's own fine print: it previously suggested Kallweit & Wood (1982) refines the classic quarter-wavelength figure directly, but that paper's actual finding is about a different, broader-bandwidth question this site doesn't otherwise address — the correct citation for the more precise same-question refinement is Chung & Lawton (1995), now pointing to the new comparison on Ricker Wavelet's own chart. No formula, input, or result changed on the Tuning Thickness calculator itself — wording only.

Added Ricker Wavelet to Geophysics' Seismic Resolution section, alongside the existing Dominant Wavelength, Vertical Resolution (Tuning Thickness), and Horizontal Resolution (Fresnel Zone) calculators. Where those three compute a single number from a bed's velocity and the seismic wavelet's dominant frequency, this one shows the actual wavelet shape itself — the classic, textbook zero-phase pulse (one central peak flanked by two smaller negative side lobes) that every one of those other three calculations implicitly assumes but never actually draws. Enter a dominant frequency and a time to evaluate, and it reports the wavelet's amplitude at that instant plus its dominant period, charting the full shape across a fixed time window. A companion "wedge tuning curve" chart (composite reflection amplitude vs. bed thickness, building on the same wavelet math) was investigated for this same session but not shipped: the numerically exact peak of that curve, worked out directly from this same formula, sits at a noticeably different bed thickness than the already-published quarter-wavelength "tuning thickness" figure, and no sufficiently authoritative source could be found to reconcile the two with confidence — see this calculator's own citation notes for the disclosed reasoning. Deferred for a future session rather than shipped with an unresolved discrepancy.

Added Directional Wellpath Profile to Drilling's Directional section — a genuinely new capability, not just another calculator. Every directional calculator this site has offered so far (Minimum Curvature Survey Calculation, Dogleg Severity, and the rest) works on one pair of adjacent survey stations at a time; this one takes an entire pasted survey — as many Measured Depth/Inclination/Azimuth stations as you have — and chains that same minimum curvature math station-by-station into a full 3D wellbore trajectory, reporting the final depth, total horizontal displacement, and the single worst dogleg severity found anywhere in the survey. It also draws a connected vertical-section chart of the whole path (depth increasing downward, the standard convention), the first chart on this site to draw a line through a pasted table of points rather than just individual markers — everywhere else that plots pasted data (P/Z Plot, the Havlena-Odeh straight line, and others) still shows points only, since connecting them wouldn't mean anything for those; here it does, because a wellbore survey is a physically ordered path. Uses the exact same formula, and the same primary reference, as the existing single-pair Minimum Curvature Survey Calculation — nothing about the underlying math is new, just the ability to run it down a whole survey at once and see the result plotted.

The Crossplots page's Pickett Plot mode now has a fourth adjustable field, "n (saturation exp.)", alongside the existing Rw/a/m fields — it controls the saturation exponent used by the plotted water-saturation reference lines. It defaults to 2.0, the standard textbook value already used before this change, so nothing looks different unless you actually adjust it.

Added a Horner Plot chart to Pressure Transient Analysis (Reservoir), plotting your pasted shut-in pressure readings against the log of the Horner time ratio alongside the fitted straight line the calculator already uses to derive permeability and extrapolated reservoir pressure (P*). This is the site's first chart with a genuinely logarithmic, right-to-left-decreasing horizontal axis — the standard convention for this kind of plot, where the fitted line's intercept (P*) sits at the right edge of the chart rather than the left. No calculator, formula, or result changed — this is a visualization addition only.

The "Sensitivity Analysis" tornado chart — introduced last on Fracture Gradient (Eaton 1969), ESP Total Dynamic Head (TDH), and Internal Rate of Return (IRR) — is now available on every calculator on the site. After calculating a result, look for the button next to Formula Derivation and Copy Result. Two small fixes came out of rolling this out broadly: a couple of calculators offer a numeric "which correlation to use" selector (e.g. Gas Z-Factor's choice of Hall-Yarborough vs. Dranchuk-Abou-Kassem) — those selector fields are now correctly left out of the sensitivity chart, since nudging them up and down doesn't mean anything physically. And a date-based calculator (Primary Term Expiration) was fixed after briefly showing an error when the new chart tried to load — it now correctly shows a short explanation instead, since a calculated date isn't the kind of result a sensitivity chart applies to. A small number of calculators whose only input is a pasted table of data (rather than individual values) will show a short note that sensitivity analysis doesn't apply to them, rather than an empty chart.

Fixed a real bug in Internal Rate of Return (IRR)'s new Sensitivity Analysis chart: for a project where the entered numbers make IRR itself unsolvable (an extremely high cash-flow-to-investment ratio, shown as "No root found"), the sensitivity chart was still computing and displaying bars — but every one of them was comparing against that meaningless zero result, not a real IRR value, so the numbers shown were not trustworthy even though they looked like normal ones. The chart now recognizes this case directly and shows a plain explanation instead of misleading bars. No other calculator's sensitivity chart was affected by this specific bug, but the same underlying check now protects all of them going forward.

Added a "Sensitivity Analysis" tornado chart to 3 calculators: Fracture Gradient (Eaton 1969), ESP Total Dynamic Head (TDH), and Internal Rate of Return (IRR). After calculating a result, click the new button to see, at a glance, which of your inputs the result is actually most sensitive to — each input is nudged up and down by a realistic amount around the value you entered, holding everything else fixed, and the resulting swing in the result is drawn as a horizontal bar; the longest bars are the inputs worth double-checking or refining first. When nudging an input in a given direction would push it into a range the calculator itself flags as invalid (for example, a pump intake pressure high enough to exceed the pump's own setting depth), that side of the bar is shown as a dashed "guard rail" marker instead of a misleading number. This is the first of a small, deliberately limited rollout — more calculators will get this treatment as it's proven out further.

Added Mud-Window Plot to Geomechanics — a genuinely new kind of chart for this site: instead of a single computed value, it plots pore pressure and fracture gradient as continuous curves running down a depth track, shading the safe mud-weight window between them, with a marker for your planned casing shoe depth. This is a visualization of two well-established methods already on this site (Eaton Pore Pressure and Fracture Gradient (Eaton 1969)), not a new formula — both curves are computed from the exact same math those two calculators already use, applied across a single representative pressure zone from surface down to the depth you specify, rather than to real logged data at multiple depths (a bigger capability, plotting actual measured survey data along a depth track, remains a planned future addition). It also grounds the chart in a plain number: the width of the safe window at the bottom of the plotted interval, so you're not left reading pixel positions off a chart alone.

Added an interactive chart to 4 existing calculators that back-solve a value from a set of pasted data points: P/Z Plot (Gas Material Balance), Material Balance — Havlena-Odeh Straight Line, Cementation Exponent Back-Solve, and Saturation Exponent Back-Solve. Each chart now plots your own pasted data points alongside the calculator's fitted trend line, so you can see at a glance how well your data actually fits a straight line (or, for the two Pickett-plot calculators, the fitted curve) instead of judging fit from the R² number alone. No calculators, formulas, or results changed — this is a visualization addition only.

Added Google Analytics 4 alongside this site's existing Plausible analytics — not a replacement, both now run together. Worth stating plainly, since a past changelog entry here specifically called out that Plausible collects usage analytics without cookies or a cookie banner: this addition does introduce cookies (Google Analytics 4 sets its own tracking cookies), a real change from how this site has operated until now. The owner made a deliberate decision not to add a cookie-consent banner alongside it.

Added Pipeline Pressure Drop (Multiphase) to Production Engineering, completing the Multiphase Flow section and, with it, this site's originally-planned Production Engineering buildout. This calculator estimates the total pressure drop along a horizontal (or close to horizontal) gas-liquid gathering pipeline, using the same well-established Beggs-Brill correlation already powering Multiphase Gradient (Beggs-Brill) for vertical wells — but simplified for a flat pipeline rather than a vertical wellbore, since a horizontal line has no elevation change to account for. One small, honest side effect of that simplification: gas-liquid surface tension, an input the vertical calculator needs, turns out to have zero effect on a horizontal pipeline's result, so this calculator simply doesn't ask for it, rather than including a field that would silently do nothing. Enter representative flow conditions and a pipeline length, and it estimates the total pressure drop over that length.

Added Hydrate Risk Estimate to Production Engineering's Multiphase Flow section. Gas hydrates — ice-like solids that can form from water and natural gas at high pressure and low temperature — are a real risk of plugging flowlines, especially in cold-weather or subsea gathering systems; the standard way to prevent them is injecting an inhibitor chemical (methanol or MEG/glycol) into the water phase, which lowers the temperature at which hydrates form. This calculator estimates how much that temperature is lowered for a given inhibitor concentration, using the well-established Hammerschmidt equation, so a quick field estimate is possible without needing the full hydrate pressure-temperature chart. Enter the inhibitor's two standard constants (this site provides both the methanol and MEG values directly) along with the concentration, and it estimates the resulting protection. Worth noting for anyone comparing sources: reputable references disagree on exactly how this formula's stated concentration limit should be measured, and this calculator discloses both interpretations rather than silently picking one.

Added a new Multiphase Flow section to Production Engineering with 2 calculators. Critical Velocity (Erosional) flags the velocity above which flow through piping, chokes, and fittings risks erosion damage, per the widely-used API RP 14E guideline. Turner Liquid Loading answers the opposite kind of question for a gas well: the minimum gas velocity — and corresponding minimum gas rate — needed to keep produced liquid droplets moving up and out of the well, rather than falling back down and restricting flow (a real, common late-life problem called liquid loading). This calculator's underlying formula needed unusually careful attention: two different published versions of "the Turner equation" exist with two different unit conventions, and rather than picking one, the constant was independently re-derived from first principles (the same physics Turner himself used — a force balance between gas drag on a liquid droplet and its weight, combined with the largest droplet size that survives without breaking apart) and cross-checked two different ways before being used here. The result also confirms which version of the formula is standard industry practice: Turner's own original theoretical model, it turns out, under-predicted real field data, and the version actually used in practice includes his own recommended 20% upward correction — which is what this calculator implements.

Added a new Surface Facilities section to Production Engineering with 3 calculators. Choke Flow (Gas) and Choke Flow (Liquid) estimate how much gas or liquid a wellhead or surface choke will pass at a given upstream/downstream pressure — Choke Flow (Gas) automatically figures out whether flow through the choke is "sonic" (the choke is fully choked, and further reducing downstream pressure won't increase the rate) or "subsonic," and uses the correct physics for each; Choke Flow (Liquid) covers the same question for a liquid-only stream. Both are deliberately single-phase: a well producing significant gas and liquid together through the same choke needs a different, more complex kind of correlation this site doesn't build, and both calculators say so directly rather than quietly giving a wrong answer for that case. Separator Residence Time checks a simple but important separator-sizing question — how long a given liquid volume actually spends in a separator at a given flow rate — and flags whether that falls inside the standard 1-4 minute design range used across the industry. The Choke Flow (Gas) calculator's worked example is reproduced directly from a real textbook problem with a published numeric answer, one of the few calculators on this site to reach that higher confidence tier.

Added Nodal Analysis: Operating Point to Production Engineering, launching a new Nodal Analysis section — a genuinely new kind of tool for this site, not just another single-value calculator. Rather than computing one number from entered inputs, it plots two curves on the same chart — how much a well's reservoir can supply at a given bottomhole pressure (using the existing Vogel IPR equation), and how much pressure the wellbore itself requires to lift a given rate to surface (using the existing Flowing Bottomhole Pressure / Tubing Traverse calculation) — and marks the point where they cross. That crossing point is the well's actual operating rate and pressure: the two curves have to agree, since the reservoir and the wellbore are the same physical system. If the two curves never cross across the full range checked, the well cannot flow as configured under those inputs, and the calculator says so directly rather than returning a meaningless number. This first version pairs one specific reservoir model (Vogel) with one specific wellbore model (single-phase liquid Tubing Traverse); covering the site's other inflow and multiphase-flow models together is a larger, separate future addition. This also unblocks two ideas that were previously investigated and deliberately left unbuilt for lacking exactly this kind of tool — Gas Lift Injection Rate and Jet Pump Flow Rate — both of which can now be revisited using the same curve-crossing approach.

Added Multiphase Gradient (Beggs-Brill) to Production Engineering's Tubing Performance section — a significant new capability, not just another calculator. Every calculator this site has offered so far for pressure behavior in tubing has assumed a single fluid phase; this one handles a well producing both gas and liquid together, the normal situation for most real producing wells, and estimates how pressure changes with depth by first working out which of several distinct two-phase flow patterns applies (essentially, how the gas and liquid arrange themselves inside the pipe — as separate layers, as slugs, or as a fine mist) and then applying the physics appropriate to that pattern. This is genuinely the most involved calculator on the site, reflecting how much more complex two-phase flow physics is than the single-phase case Flowing Bottomhole Pressure (Tubing Traverse) already covers — for now it's scoped to vertical wells and evaluates conditions at a single point rather than tracing pressure all the way down a well, which remains a larger undertaking for a future update.

Added a new Tubing Performance section to Production Engineering with 5 calculators. Gas Velocity and Liquid Velocity report how fast gas or liquid is actually moving inside the tubing — useful for checking against erosion limits. Reynolds Number and Friction Factor (an explicit, non-iterative formula from Haaland, 1983) work together to characterize how much friction a flowing fluid experiences against the tubing wall. All four feed into the fifth and main addition, Flowing Bottomhole Pressure (Tubing Traverse), which estimates the pressure at the bottom of a well from a measured wellhead pressure — tracing the pressure change down the tubing string from the weight of the fluid column plus friction loss, and reporting both the final bottomhole pressure and the total pressure drop along the way. This fills a real gap: several of this site's existing inflow-performance calculators (Productivity Index, Vogel, Standing, Fetkovich, Composite IPR) need bottomhole pressure as an input, and this is the first calculator here that estimates it from more easily measured surface data instead of requiring a downhole gauge reading. Covers single-phase liquid flow only for now; a version that handles wells producing both gas and liquid together is a larger, separate undertaking planned for later.

Added Composite IPR (Beggs) to Production Engineering's Inflow Performance section — a single calculator that covers a well's inflow performance across its full producing life, from initial above-bubble-point conditions through depletion below it. It automatically switches between a straight-line relationship (like the existing Productivity Index calculator) while the well is above its bubble point, and a Vogel-shaped curve (like the existing IPR — Vogel's Equation calculator) once it drops below — the two pieces are proven, not just assumed, to meet up exactly at the bubble point, both in value and in slope, so the combined curve is genuinely smooth rather than kinked at the transition. Enter the same productivity index already produced by the Productivity Index calculator (they link to each other) along with reservoir pressure and bubble point pressure, and this calculator figures out which regime applies on its own. Doesn't cover wells producing meaningful water alongside oil — that needs a different, more involved formula this site doesn't build yet.

Added two calculators to Production Engineering's Inflow Performance section: Fetkovich IPR (Oil Wells), which estimates a well's deliverable oil rate and open-flow potential from a single backpressure test point — the same well-tested equation form already used by the existing Gas Well Deliverability calculator, but Fetkovich's own separate finding that it also fits oil wells below the bubble point; and Standing IPR (Flow-Efficiency Modified), which extends the existing Vogel IPR curve to account for a well's actual skin damage or stimulation. Standing IPR reads its Flow Efficiency value from the Skin Factor calculator's own result (they link to each other) rather than recalculating it, the same "run one calculator, carry its result into the next" pattern already used between the Rod Pump Displacement and Rod Pump Efficiency calculators.

Added Hydraulic Lift Piston Pump Flow Rate to Production Engineering, completing the site's Artificial Lift toolset (ESP, Gas Lift, Sucker Rod Pump, Plunger Lift, and now Hydraulic Lift all covered). This calculator estimates a downhole hydraulic piston pump's theoretical daily fluid displacement from its piston and connecting-rod sizes, stroke length, and pumping speed. Unlike the existing Rod Pump Displacement calculator, a hydraulic piston pump produces fluid on both its upstroke and downstroke, not just one — so this one accounts for the connecting rod taking up part of the pump's swept volume on one side of that cycle, a real mechanical difference that changes the result, not just the name. A related idea, jet pump flow rate, was looked into and deliberately not built: sizing a jet pump genuinely requires matching a well's own inflow performance against a family of pump performance curves rather than solving a single equation, the same reason this site has stayed out of Gas Lift Injection Rate.

Added Plunger Lift Minimum Casing Pressure to Production Engineering — the surface casing pressure a plunger-lifted well needs to lift its plunger and accumulated liquid slug all the way to surface, from the plunger's weight, the tubing it travels in, the slug's size, and the pressure the well is discharging against. This is the plunger-lift counterpart to the existing Gas Lift Valve Pressure calculator's same kind of force-balance approach. A related idea, plunger rise/fall velocity, was looked into and deliberately not built: the classic field numbers for it (roughly 1,000 ft/min rising, faster falling) come from fitting historical field data, not from a formula that predicts velocity from a well's own parameters — the same reason this site has stayed out of Gas Lift Injection Rate and Pump Fillage. A commonly quoted "minimum gas-liquid ratio" rule of thumb was also checked and set aside for now, since the number behind it looks field-fitted rather than genuinely derived. This is the fourth of five planned lift-method additions (Hydraulic Lift is the last).

Added two Sucker Rod Pump calculators to Production Engineering: Rod Pump Displacement, the theoretical (100%-fillage) daily fluid volume a beam pump's plunger diameter, stroke length, and pumping speed can displace; and Rod Pump Efficiency, which compares an actual measured production rate against that theoretical figure to show how much of the pump's capacity is really being realized. Feed Displacement's own result directly into Efficiency for a quick pump-performance screen. A related idea, "pump fillage," was looked into and deliberately not built — what that term actually means in the field is reading a dynamometer card's shape to spot the exact point fluid load transfers onto the pump, which is a visual/judgment call, not a plug-in formula, the same reason this site has stayed out of things like mud-log lithology calls. This is the third of five planned lift-method additions (Plunger Lift and Hydraulic Lift are next).

Added Gas Lift Valve Pressure to Production Engineering — checks the casing (injection-gas) pressure needed to open a nitrogen-charged gas lift valve at depth, from the valve's dome charge pressure, the tubing pressure it's working against, and its port-to-bellows area ratio. Useful for confirming a valve is set to open at the intended point in a gas lift string, or troubleshooting one that isn't. This calculator intentionally doesn't include the correction for how a valve's charge pressure changes between its shop-test temperature and actual well temperature — that step needs a manufacturer's own nitrogen chart, and the reference material we could access to build it into this tool directly didn't agree with itself on the details, so it was left out rather than guessed at. This is the second of five planned lift-method additions (Sucker Rod Pump, Plunger Lift, and Hydraulic Lift are next).

Added a new Production Engineering discipline, launching with three Electrical Submersible Pump (ESP) calculators: ESP Total Dynamic Head (TDH), the total head an ESP pump must generate — combining net vertical lift, tubing friction loss, and wellhead backpressure; ESP Pump Intake Pressure (PIP), which confirms a pump is running with adequate suction pressure from a casing pressure reading and a fluid-level survey; and ESP Horsepower, which sizes the required pump brake horsepower from flow rate, TDH, fluid gravity, and pump efficiency. All three link to each other for a full ESP sizing workflow. This is the first of five planned lift-method additions (Gas Lift, Sucker Rod Pump, Plunger Lift, and Hydraulic Lift are next).

Fixed a visible layout glitch on the homepage: expanding the "How to use this site" guide could shift the discipline tiles above it from a 6-column row to 5 for a moment, since the guide's extra height triggered a scrollbar that nudged everything else over. The tiles now hold their layout regardless of whether that guide is open or closed. Also moved the site tagline back next to the "B" logo at the top of the homepage instead of the header, so the header stays a single clean line on every page. No calculators, formulas, or values changed.

Clearer site identity, and a real fix to the homepage's getting-started guide. "BauerCalc" and its tagline ("Subsurface Engineering Reference Platform") now appear together in the header on every page, not just as a large block on the homepage — the homepage itself now leads with search and the discipline list instead of a big title. The homepage's "New to BauerCalc? How to use the site" guide previously needed two clicks to actually see its content if you'd dismissed it once before (one to bring the section back, a second to expand it) — it's now a single control, one click, and stands out with a gold border matching the search box. No calculators, formulas, or values changed — this is a navigation and homepage-layout improvement only.

Reworked the homepage so calculators are easier to find, faster. The discipline browse tiles now appear right after the search box, with a clear "Browse by Discipline" heading above them, instead of below a large "How to use this site" panel; that guide is now a compact, collapsed-by-default "New to BauerCalc?" section further down the page (still covers formation defaults, IMP/MET units, and LAS files in full — nothing was removed, just relocated). The site name and tagline at the top are also larger and more prominent. No calculators, formulas, or values changed — this is a homepage layout improvement only.

A real performance improvement for every visitor: the core page every visitor downloads on first load is now about 85 KB smaller (roughly a fifth lighter). Several less-frequently-visited pages — Pay Table, Crossplots, Unit Converter, Load LAS, Literature, Reference, About, Disclaimer, and this Changelog — now download their own code only when you actually open them, instead of every visitor paying for all of them up front regardless of which pages they ever visit. Nothing changed about what any of these pages look like or how they behave; this is a behind-the-scenes loading-speed improvement only.

Made search and the homepage easier to use, especially on a phone. Search now ranks the calculator whose name actually matches your query first, instead of sometimes burying it behind unrelated results that only shared a loose tag; weaker fuzzy matches are now visually separated under "Other possible matches". On a phone, the homepage's "How to use this site" guide now starts collapsed to one tappable line, so the search box and discipline list are visible immediately (unchanged on a full-size screen), and it no longer repeats the same disclaimer sentence a third time (still shown on first visit and in the footer). No calculators, formulas, or values changed.

Polished the site's shared interaction and visual system. Keyboard focus is now clearly visible everywhere — tabbing through a page previously relied on the browser's own faint default outline, which was hard to see on the dark theme and easy to miss on light; every button, link, and field now shows a clear blue ring around whatever's currently focused, kept visually distinct from the gold used for a selected mode or an active tab so the two never get confused with each other. Secondary buttons (Share, Export, Cancel, and similar) now stand out more clearly as clickable, instead of blending in with the page's own decorative dividers and borders. A few small low-emphasis controls (the dismiss button on the homepage's help panel, the "Details" link on a loaded worked example) now share one consistent style instead of each being styled slightly differently. No calculators, formulas, or values changed — this is a visual and accessibility polish pass only.

Reworked the site's top navigation and mobile menu. On desktop, the last item in the navigation bar could get visually cut off on smaller laptop screens (around 1440px wide) — fixed by moving less-frequently-used pages (About, Disclaimer, Changelog) into a "More" menu, with everything reachable in one click either way. On mobile, the header used to show the entire desktop navigation squeezed into several rows before you could see any actual page content — it's now just the BauerCalc logo, a search box, and a menu button, with every page (including the discipline browse pages) and the Imperial/Metric unit switch moved into that menu. On a discipline's browse page on mobile, "Select a calculation from the sidebar" is now a real "Browse [Discipline] Calculators" button that opens the menu directly, instead of pointing at a sidebar that isn't currently visible. No calculators, formulas, or values changed — this is a navigation and layout improvement only.

Clearer calculator results: a value and its unit (like "0.354 fraction") could visually run together with no space between them — fixed across every calculator, including when copying a result or reading it with a screen reader, not just how it looks. Calculators with several outputs (like Principal Stress Summary's six) now clearly highlight the main result in large type and show the rest as a compact, readable list underneath, instead of every number being the same oversized size. When a Range, Batch, or Depth-series calculation skips a scenario or row because a value was missing or invalid, that notice now appears right next to the results it's about, instead of up near the input fields where it was easy to miss. No calculators, formulas, or values changed — this is a display and readability improvement only.

Cleaned up a source of on-page confusion: every calculator page used to show two separate sets of Standard/Range/Batch/Depth mode buttons — one near the top of the page, one inside the calculator card itself — that did the same thing and could look out of sync with each other. There's now just one mode selector, placed right below the calculator's name and formula so it reads clearly as part of that calculator (not above it), and it now stays visible near the top of the screen as you scroll down through a long calculator's assumptions, limitations, and references, instead of disappearing once you scroll past it. On a phone, the mode selector also takes up noticeably less permanent screen space than before. No calculators, formulas, or results changed — this is a navigation and layout improvement only.

Fixed a set of real Imperial-mode display bugs found by a project-wide audit of how calculators convert between Imperial and Metric units: 7 fields across 6 calculators in 4 disciplines (Fluid Properties, Petrophysics, Drilling, and Reservoir) were showing an unconverted raw number under an Imperial unit label instead of the correctly-converted value — off by roughly 3× to 35× depending on the field. Affected: Material Balance — Havlena-Odeh Straight Line's underground-withdrawal column; Gas Compressibility's pseudo-critical pressure input; Oil Density and Cuttings Slip Velocity's density fields; Flow Capacity's two thickness-scaled outputs; and Volumetric Reserves / Remaining Reserves' phase-dependent resource/reserves fields (the latter now also has its own Oil/Gas phase selector, matching Volumetric Reserves, so it can convert correctly too). Metric mode was already correct for all of these — only Imperial mode was affected. A permanent automated check now runs on every future change to catch this entire class of bug before it ships again.

A real performance improvement for anyone on a slow or metered connection: the first page you navigate to within BauerCalc after loading now downloads about 20 KB of supporting data instead of about 1.2 MB — a behind-the-scenes fix to how the site hands off calculator content when you click between pages. Nothing changed about what you see or how the site behaves, just how much has to download to get there.

Keyboard and screen-reader accessibility improvements: the discipline tiles on the home page and a calculator's formula-derivation toggle can now be reached and activated with the keyboard (Tab, then Enter or Space), not just a mouse click; the breadcrumb trail at the top of a calculator page is now keyboard-activatable too; input fields with a warning message now correctly announce that message to screen readers; and the Range/Batch/Depth-series input modes' fields now have proper labels a screen reader can announce, matching what Standard mode already had. No visual change for anyone using a mouse.

The site's fonts now load from BauerCalc itself instead of Google's font service — one fewer external connection your browser has to make on every page, and nothing is sent to Google just to render text. Text looks exactly the same; this is a behind-the-scenes performance and privacy improvement, not a visual change.

Fixed a bug where switching input modes (Standard/Range/Batch/Depth) using a calculator's own mode tabs could leave the previous mode's result on screen instead of clearing it — so it was possible to switch modes and see a stale result that looked like it belonged to the new mode. Switching modes now always clears the previous result, no matter which mode-switch control you use.

Fixed a correctness bug in the Range/P10-P90 and Batch input modes: a Range scenario left blank (with no standard-mode value to fall back on) previously computed as if you'd entered zero, and a Batch paste with one bad or missing cell in a column could silently shift every row after it into the wrong column alignment — both could produce a plausible-looking but meaningless result with no indication anything was wrong. A Range scenario or Batch row with a missing or non-numeric value is now skipped and clearly noted, with a count, instead of silently computing on a fabricated value. Also, Standard, Range, and Batch results now flag when an input value is outside the expected physical range or a correlation's fitted range — the same check Depth-series results already showed.

Charts and crossplots now redraw correctly when the browser window is resized or a phone is rotated, instead of staying stretched or blurry until something else on the page changed. On the Crossplots page, the plot-type buttons (Neutron-Density / Pickett / RHOB) no longer run off the edge of the screen on a phone, and the plot's control panel now sits above the plot instead of squeezing it into a narrow strip. A long chart title (like Casing Collapse Pressure's "Collapse Regime Map") now wraps cleanly instead of clipping at narrow widths.

Continuing the mobile-usability work from the last update: the Range/P10-P90 mode's low/mid/high fields now stack into a clearly-labeled vertical list on a phone instead of squeezing into an unreadable row, and a calculator's paste-a-table input (used by calculators like Average Thickness & Porosity and Material Balance — Havlena-Odeh Straight Line) now gets a full-width, larger paste box and a preview table that scrolls sideways instead of clipping. Batch and Depth-series input modes were checked directly on a phone screen and already worked fine, so they're unchanged. Charts and crossplots are next.

The site is now usable on a phone. The sidebar collapses behind a menu button instead of squeezing every page into a narrow sliver, the header no longer crowds itself on discipline pages, and each calculator's two-column layout stacks into one readable column. This is the first phase of an ongoing mobile-usability effort — calculator input modes like Range/Batch and charts still get more polish in future updates.

The decline-curve calculators (Hyperbolic Decline, Harmonic Decline, EUR from Decline Parameters) and the cash-flow calculators (Economic Limit Rate, and the variable-cash-flow NPV/IRR/Payback Period trio) now link directly to each other, with guidance on how to combine them for type-curve well economics — project production with a decline curve, then value it with the cash-flow tools.

Added five more Economics calculators: Modified Internal Rate of Return (MIRR), a more reliable alternative to IRR for a cash flow with a mid-life negative year (like a major workover), which can otherwise make IRR ambiguous or undefined; Profitability Index, in both level and variable-cash-flow versions, for ranking competing projects by value created per dollar invested rather than by total NPV — useful when capital itself, not project acceptability, is the constraint; and Expected Monetary Value (EMV), in both a standard two-outcome (commercial success / dry hole) form and a general multi-outcome form for a decision with more than two scenarios. EMV is also commonly called "Risked NPV" in the industry — both names point to the same calculator here, and it deliberately avoids a known-unreliable shortcut (simply multiplying NPV by chance of success) that silently ignores the cost of a dry hole.

Added five Economics calculators covering capital efficiency and field-level margin: CAPEX per Foot and F&D (Finding & Development) Cost, two standard capital-efficiency ratios for comparing drilling spend and reserve-replacement spend across wells or periods; Netback, which shows the actual cash margin a well earns after royalty, operating, and transportation/processing costs — plus a Netback Margin percentage on the same result; Price Differential, a quick way to see how a wellhead price compares to a benchmark like WTI; and Recycle Ratio, which combines Netback and F&D Cost into the standard "are we recovering our reserve-replacement spending" screen. Netback is deliberately pre-tax (a real, currently-used industry variant, not a shortcut) — its own result panel says so directly.

Added three Economics calculators built around the same break-even relationship as the existing Economic Limit Rate tool: Breakeven Oil Price and Breakeven Gas Price, which find the price below which a well at a given production rate stops covering its fixed operating cost — the price-based complement to Economic Limit Rate's rate-based break-even; and Breakeven EUR, which asks a different question — how much cumulative volume (not rate) a well needs to recover to cover its total capital and operating cost. Breakeven EUR is deliberately a simplified, undiscounted screening number (it doesn't apply time value of money or assume any particular production decline schedule) — its own result panel says so directly, and it links to the EUR from Decline Parameters tool for comparing against an actual decline-curve estimate.

Added three Economics calculators for a genuinely variable or declining annual cash flow: Net Present Value, Internal Rate of Return, and Payback Period (Variable Cash Flow) — paste a year-by-year sequence of cash flows instead of assuming a single level amount. Real oil & gas production declines, so these are a more realistic model than the existing level-annuity NPV/IRR/Payback Period tools for most wells; the existing three remain available for a genuinely level cash flow and now link directly to their variable-cash-flow counterparts.

Added a Brittleness Index calculator to Geomechanics, alongside the existing Dynamic Elastic Moduli tool — a completion-design screen that combines Young's modulus and Poisson's ratio into a single relative-brittleness score using the widely-cited Rickman et al. (2008) method. This one comes with an unusually large disclosure: the original paper wasn't directly accessible to us, secondary sources disagree on the exact formula it describes, this tool uses the same log-derived ("dynamic") elastic values as Dynamic Elastic Moduli rather than the lab-measured ("static") values the method calls for, and the built-in normalization defaults are calibrated to the Barnett Shale specifically — recalibrate them for any other play. Read the calculator's own Assumptions/Limitations section before trusting a result from it.

Added two Drilling calculators alongside the existing Eaton Pore Pressure tool: Eaton Pore Pressure (Resistivity), which predicts pore pressure from a deep resistivity log instead of a sonic log — useful as a cross-check, or when sonic data is sparse — using the same Eaton (1975) method with its own independently-calibrated normal trend; and Corrected d-Exponent, which derives a pore-pressure indicator from routine drilling parameters (rate of penetration, rotary speed, weight on bit, bit size), corrected for mud-weight effects on drilling rate — a real-time drilling-break indicator that doesn't depend on a wireline or LWD log at all.

Added a Breakdown Pressure calculator to Geomechanics — the wellbore pressure at which a hydraulic fracture actually initiates at the wellbore wall, using the same wellbore-stress physics as the existing Critical Mud Weight and Hoop Stress (Kirsch) tools, evaluated on the tension side instead of the shear side. This is a more complete estimate than the existing Fracture Gradient tool's simpler approximation, since it also accounts for the maximum horizontal stress and pore pressure, not just the minimum horizontal stress — both link to each other so the distinction is clear. Requires a tensile strength value as an input; this platform doesn't yet have its own tool to estimate that from log data, since the common "UCS ÷ 10-12" shortcut turned out, on closer research, to likely be misattributed to the paper usually cited for it.

Added three Geomechanics calculators: Hoop Stress (Kirsch), which shows the wellbore-wall stress at a mud pressure you specify — useful for checking how much margin a planned mud weight actually has, not just whether it passes or fails the existing Critical Mud Weight threshold; Principal Stress Summary, a one-card view of a well's full stress state (vertical, minimum and maximum horizontal, and effective stress) with two commonly used stress ratios and an implied faulting-regime classification; and Safe Mud Weight Window, the standard pore-pressure-to-fracture-gradient drilling margin, which also checks whether the wellbore-collapse threshold (not just pore pressure) is the tighter lower bound in weak or high-stress-anisotropy rock.

Added four Drilling calculators for hole cleaning and pump performance: Annular Velocity (how fast fluid moves up the annulus); Cuttings Slip Velocity, which lets you choose between two widely used correlations (Chien or Moore) for how fast drilled cuttings fall back through the fluid, since the two can give meaningfully different answers on the same well; Cuttings Transport Ratio, which combines the two into a single hole-cleaning check against the standard 50% minimum guideline; and Pump (Volumetric) Efficiency, comparing a mud pump's actual measured output against its theoretical geometric output. Standpipe Pressure and Surface Equipment Pressure Loss remain on the roadmap, alongside Swab/Surge Pressure, pending a source we can verify directly.

Added two Drilling calculators for tripping operations: Pipe/Casing Displacement, the volume of mud a pipe or casing string's own steel displaces (distinct from the existing Buoyed Weight tool, which covers the force effect of that same submerged steel, not its volume); and Trip Volume, the standard trip-sheet calculation for the mud volume a rig should expect to add or bleed while running or pulling open-ended pipe, plus the equivalent mud-level change — useful for spotting a well-control problem when the actual trip tank reading doesn't match. Swab Pressure and Surge Pressure remain on the roadmap; the underlying model (Burkhardt's 1961 correlation and its descendants) needs a source we can verify directly before it's built.

Added a Gas Kick Expansion calculator to Drilling — enter a gas kick's volume and the pressure at its original depth and at a shallower depth, to see how much the kick expands (via Boyle's Law) as it migrates up the wellbore. Distinct from Reservoir's Gas Cap Expansion tool, which tracks a producing reservoir's gas cap over its production life rather than a kick over a well control event — both link to each other to make the distinction clear. Also: Kill Mud Weight's mud-weight-increase result is now labeled and searchable as "kick intensity," the term some operators use for it.

Added five Drilling calculators covering circulating and bit hydraulics: Pump Output (flow rate from pump liner size, stroke length, and speed); Reynolds Number, which checks whether flow inside the drillpipe and in the annulus is laminar or turbulent; Pressure Loss, the frictional pressure drop in the drillstring for laminar flow; Lag Time / Bottoms Up, the time for cuttings or gas to travel from the bit to surface; and Bit Hydraulics, which reports jet velocity, hydraulic horsepower, and impact force at the bit together from the same flow-rate and nozzle inputs.

Added a Well-to-Well Separation calculator to Drilling — enter two wellbores' Northing, Easting, and TVD positions to get the lateral separation, vertical separation, total 3D distance, and separation azimuth between them, for anti-collision checks and offset-well proximity screening. Distinct from Reservoir's Well Spacing (Drainage Radius) tool and Land & Ownership's Spacing/Drilling Unit Acres — both link to this new calculator to make the distinction clear. Also added three smaller Directional calculators: True Vertical Depth Subsea (TVDSS), Turn Rate (the azimuth-only counterpart to Build Rate), and Vertical Section (projects wellbore closure onto a single planned reference direction).

Added an N-Layer Depth Conversion calculator to Geophysics — paste a stack of interval velocities and their two-way-time thicknesses, one row per layer (from Checkshot Average & Interval Velocity, Interval Velocity from RMS Velocities (Dix), or offset-well control), to get a single cumulative depth for the full stack, plus an effective average velocity. Fills a gap the two existing single-average and linear-gradient depth-conversion tools couldn't cover: converting a genuine multi-layer velocity survey instead of treating the whole overburden as one velocity.

Added a Dynamic Elastic Moduli calculator to Geomechanics — enter bulk density and P-/S-wave velocity to get Young's, Bulk, and Shear Modulus. Explicitly labeled as dynamic (log/sonic-derived) moduli, with the difference from static (core-test) moduli called out directly, since wellbore-stability and frac-design work needs to know which one it's looking at. Also: Vp/Vs Ratio (Geophysics) now shows Poisson's Ratio as its own result field instead of only mentioning it in a note.

Added an Aquifer Influx (Fetkovich) calculator to Reservoir — paste a reservoir's pressure history over time, alongside the aquifer's productivity index and initial encroachable water volume, to project how much water influx a water-drive reservoir is receiving and how the aquifer's own pressure is declining over time. Completes the Material Balance toolset alongside P/Z Plot and Material Balance — Havlena-Odeh Straight Line, both of which previously assumed no water influx.

Added four Reservoir calculators: Water Drive Index, a quick ratio measuring how much of a reservoir's production is being replaced by natural aquifer support; P/Z Plot, which fits a straight line through pressure/production history to back-solve gas in place instead of requiring it as a known input; Material Balance — Havlena-Odeh Straight Line, the multi-point extension of the existing single-point Material Balance OOIP tool, using a reservoir's full production history in one fit instead of a single pressure reading; and Pressure Buildup — Horner Analysis, which derives both permeability and extrapolated reservoir pressure directly from raw shut-in pressure readings — the Skin Factor calculator previously required both as pre-solved inputs.

Added a Multi-log Average Porosity calculator to Petrophysics — paste porosity estimates from multiple logs or methods (neutron, density, sonic, NMR, core, etc.) at the same depth to get their average, useful for reconciling several readings into one representative value in normal (non-gas) zones.

Added a Saturation Exponent Back-Solve calculator to Petrophysics — paste a core sample's water-saturation/resistivity readings from a lab desaturation test, plus its measured 100%-water-saturated resistivity, to back-solve the saturation exponent (n) used in Water Saturation (Archie) from real data instead of the textbook default. Completes the pair alongside the existing Cementation Exponent Back-Solve.

Added three calculators that introduce a new "paste a table of rows" input for multi-zone data, instead of entering one value at a time: Average Thickness & Porosity and Average Water Saturation (Geology) let you paste per-zone data from several wells or intervals and get correctly-weighted average values back — no more manually working out a thickness-weighted average by hand. Cementation Exponent Back-Solve (Petrophysics) fits a Pickett-plot line through pasted porosity/resistivity points from clean, water-bearing zones to back-solve the cementation exponent (m) used in Water Saturation (Archie), instead of relying on the textbook default.

Added five Reservoir calculators covering waterflood displacement and material balance drive mechanisms: Mobility Ratio and Fractional Flow (single saturation point), the two core measures of how favorably water displaces oil; Voidage Replacement Ratio, the standard injection-vs-production pressure-maintenance surveillance metric; and Gas Cap Expansion and Oil & Solution Gas Expansion, the two drive-mechanism-energy terms used in general material balance analysis. Also: Oil Recovery Factor now shows Displacement Efficiency (Ed) as a second result — a value it was already calculating internally — and no longer asks for a porosity value it never actually used.

Added six Reservoir calculators: Volumetric Reserves, which turns an already-computed Oil or Gas in Place figure into recoverable reserves with a recovery factor; Remaining Reserves, a quick reserves-minus-cumulative-production update; Well Spacing (Drainage Radius), which converts a target per-well drainage area into a minimum non-interfering distance between wells — distinct from Land & Ownership's spacing-unit acreage and Drilling's separate wellbore-separation concept; Radial Flow, the steady-state Darcy inflow equation for a well draining a circular area (complementing the existing linear-flow calculator); and Water Cut and Water-Oil Ratio, the two standard water-handling production metrics.

Added a Pore Volume & Hydrocarbon Pore Volume calculator to Reservoir — enter drainage area, net pay, porosity, and water saturation to get both values directly, without needing to run a full Oil or Gas in Place calculation first.

Added six Petrophysics calculators, completing the discipline's planned expansion: Bulk Volume Hydrocarbon and Irreducible Water Saturation (Swirr) — a quick way to predict the water saturation floor in an uncored zone from a calibrated bulk volume water value; Apparent Water Resistivity (Rwa), a rapid hydrocarbon quick-look indicator; Formation Water Resistivity from SP, which derives Rw directly from the SP log instead of a salinity value; an M-N Lithology Plot for sonic/density/neutron mineral identification; and a Thomas-Stieber calculator for estimating laminated shale volume from a neutron-density crossplot.

Added two Petrophysics calculators: Water Saturation (Waxman-Smits), a shaly-sand method that corrects for clay conductivity using core cation-exchange-capacity data rather than a shale-resistivity estimate, and Apparent Matrix Density, a log-QC tool that back-solves the matrix (grain) density implied by a bulk density log reading and a known core porosity — useful for checking or refining the matrix density assumption used elsewhere.

Added a Net-to-Gross calculator to Petrophysics — enter a net and gross pay thickness to get the net-to-gross ratio, which now feeds directly into Geology's Net Rock Volume tool. Also added two new result fields to existing calculators: Clay Volume (GR Linear) now shows the Gamma Ray Index (IGR) alongside clay volume, and Water Saturation (Archie) now shows Hydrocarbon Saturation alongside water saturation — both values were already being calculated, just not previously shown.

Added a Cross Section Vertical Exaggeration calculator to Geology — enter a cross section's horizontal and vertical scale, get the exaggeration factor to report alongside the section.

Added two more Geology calculators: Gross Rock Volume and Net Rock Volume, the starting steps of a reservoir volumetric estimate — enter an area and gross thickness (plus a net-to-gross ratio for the net version) to get a rock volume in acre-feet or cubic meters.

Added two more Geology calculators: Target Window Thickness, which checks how much vertical room a landing target offers between its top and base picks, and Formation Top Projection, a "dead reckoning" tool that projects a formation top's expected depth ahead of the bit from a known reference depth, distance, and dip.

Added two Geology calculators: Structural Closure (Trap Height), which finds the maximum column height a trap's geometry can support from its crest and spill point depths, and Structure Gradient, a quick regional-dip-rate tool between two structural picks — the first of several planned additions to Geology's Structure & Mapping section.

Added a Primary Term Expiration calculator to Land & Ownership — enter a lease's effective date and primary term to find the date its primary term expires, with a built-in date picker and a clear reminder that production can extend a lease beyond this date.

Your imperial/metric unit setting is now remembered across visits, the same way your light/dark theme already is.

A failed calculation now always shows a clear error message, in every input mode — Standard, Range/P10-P90, Batch, and Depth Series — instead of only Standard mode. Loading a shared link or a "Load example" that fails to calculate now also shows an error instead of failing silently.

Added five more Geology calculators, completing the discipline's initial buildout at eleven: TVT/TST Correction for wellbore deviation, Fault Throw, Heave & Net Slip, Shale Gouge Ratio (a fault-seal risk indicator), Rock-Eval Source Rock Indices (Production, Hydrogen, and Oxygen Index), and a Sclater & Christie Decompaction tool for burial-history reconstruction.

Added a new Geology discipline with six calculators: Three-Point Problem (strike & dip from three points), Apparent Dip from True Dip, Isopach from Isochore Thickness, Formation Top Subsea Depth, ΔlogR Total Organic Carbon (a log-derived source-rock richness estimate), and a Lopatin Time-Temperature Index tool for thermal-maturity screening.

Added a new Depth Series input mode to Clay Volume (GR Linear), Neutron-Density Porosity, and Water Saturation (Archie) — load a LAS file and run the calculation across every depth in the log at once, with results shown as a table and available as a CSV download.

Fixed a bug in LAS file loading where, if one log curve had a gap (a "null" reading) at a different depth than another curve, values from mismatched depths could be silently paired together. This affected the Pay Table tool and the crossplot charts on the Crossplots page.

Search is now faster and more forgiving of typos — press Ctrl+K (or Cmd+K) from anywhere to search all calculators.

Every calculator can now export a report. A new "Export Report" button lets you pick which sections to include — inputs, results, chart (where available), description, variables, assumptions, limitations, region notes, and references — and download the result as a PDF or a PNG image. Reports render in a clean, print-friendly light layout regardless of your site theme, and every export includes the site disclaimer.

Added interactive charts to six calculators: Eaton Pore Pressure and Casing Collapse Pressure (Drilling), IPR — Vogel's Equation and the Hyperbolic Decline forecast (Reservoir), Water Saturation (Archie) (Petrophysics), and the Shuey AVO Approximation (Geophysics). Each chart updates live as you change inputs, matches your light/dark theme, and follows your imperial/metric unit setting.

Added four Land & Ownership calculators, completing the discipline's Spacing and Revenue sections: Spacing/Drilling Unit Acres and Horizontal Well Allocation Factor (Spacing), plus Revenue Payment Estimate and Division Order Decimal Verifier (Revenue).

Merged Annual Rental and Delay Rental into a single Lease Rental calculator, and corrected an outdated federal lease rental rate figure in the process — the two tools turned out to describe the same underlying payment (private "delay rental" and federal/state "annual rental" are the same mechanism under different names, not two different things).

Added two Lease Calculations tools to Land & Ownership: Lease Bonus and Lease Rental.

Added a new Land & Ownership discipline with seven calculators: Gross Acres to Net Acres, Net Mineral Acres, Working Interest Share, Net Revenue Interest, Royalty Interest, Overriding Royalty Interest (ORRI), and Back-in / Carried Interest. Net Revenue Interest has moved here from Economics — the link is unchanged if you'd bookmarked or shared it — and Economics now stays focused on project valuation (NPV, IRR, payback, LOE, economic limit rate).

Added a new Economics discipline with six calculators: Net Present Value, Internal Rate of Return, Payback Period (simple and discounted), Net Revenue Interest, Lease Operating Expense per Unit, and Economic Limit Rate. The Economic Limit Rate tool now links directly to the existing EUR from Decline Parameters calculator in Reservoir, so you can derive the economic cutoff rate it needs instead of guessing it.

Added two Fluid Properties calculators: a Wilson equilibrium-ratio (K-value) tool, and a compositional bubble-point-pressure tool built on top of it — a different method from the existing bubble point calculator, useful when you know a mixture's composition rather than its API gravity and gas-oil ratio.

Added six more Fluid Properties calculators: oil density, gas viscosity, gas compressibility, and a new set of water-property tools — water compressibility, water formation volume factor, and water viscosity.

Added a Fluid Properties discipline for PVT correlations. New calculators: gas Z-factor (Hall-Yarborough and Dranchuk-Abou-Kassem), oil viscosity (dead, saturated, and undersaturated), and undersaturated oil compressibility. The existing PVT tools — black-oil PVT, bubble point pressure, gas FVF, and gas-oil ratio — now live in this discipline (their links are unchanged). Inputs on these tools now show a gold advisory when a value falls outside the range the correlation was originally fitted to.

Added a "Load example" button to every calculator that pre-fills realistic, verified values and calculates them, so you can see how a tool works before entering your own data. A small badge shows whether each example comes straight from published literature or was independently verified against the calculator's own formula.

Added a "Report an issue" link on every calculator page, and this changelog.

Added privacy-friendly usage analytics (Plausible) — no cookies, no personal data collected, no cookie banner required.

Every calculator now has its own dedicated, search-indexed page and a shareable link that reproduces your exact inputs (previously the entire site was one URL).

Added a consulting-services link, a new About page, and a fully rewritten Disclaimer (11 sections, up from 7) covering software limitations and external references.

Fixed a display-precision bug affecting batch-mode results, sensitivity sliders, and input range-warning messages.

Fixed a display-precision bug affecting 79 of 100 calculators, where some results were rounded to the wrong number of decimal places or shown in scientific notation unnecessarily.

Added a pore compressibility correlation (Newman 1973, sandstone & limestone) to Petrophysics.

Geophysics: added Lambda-Rho/Mu-Rho and Gardner density-from-velocity tools; moved the Rw-vs-Temperature calculator into Petrophysics, next to the related salinity tools.

Geophysics: added seismic resolution and attribute tools — dominant wavelength, tuning thickness, Fresnel zone radius, instantaneous amplitude/phase/frequency.

Geophysics: added AVO and elastic impedance tools — exact Zoeppritz equations, Aki-Richards and Shuey approximations, Connolly elastic impedance, AVO classification.

Geophysics: added interval-velocity and depth-conversion tools — checkshot survey, Dix equation, average velocity, Slotnick V0-k.

Petrophysics: added rock-physics tools — capillary height above free water level, the Leverett J-function, pore compressibility (Hall 1953) — and a formation-water salinity/resistivity correlation.

Redesigned dashboard search and made sidebar categories collapsible for easier navigation as the calculator library has grown.

Assumptions, limitations, and region-specific notes are now shown on every calculator page (previously present in the data but not displayed).

Reservoir: added fluid-property (PVT) tools, a material balance tool, and a gas well deliverability tool.

Added site-wide search — any calculator can now be found by name, category, or tag from anywhere on the site.

Rebranded from PetroCalc to BauerCalc.

Added the Geomechanics discipline — overburden and effective stress, wellbore stability, and compaction pore pressure.

Fixed a bug where selecting a formation could overwrite unrelated inputs with incorrect values carried over from a different discipline's calculations.

Fixed calculator inputs not pre-filling with their default values.

Drilling: added well control tools — MAASP, kill mud weight, formation integrity/LOT, kill sheet circulating pressures, kick tolerance.

Drilling: added a buckling calculator showing both sinusoidal and helical onset limits side by side, since the helical constant is genuinely unsettled in the published literature.

Drilling: expanded from 4 to 18 calculators — hydraulics, torque & drag, and casing design tools.

Added the Reservoir Engineering discipline; added a dark theme toggle (light theme is the default).

BauerCalc (then PetroCalc) launched with an initial set of Petrophysics, Reservoir, and Drilling calculators.