curve.fit changelog

New features, usability improvements, and fixes. Calculation notes highlight updates that may affect your fitted values, uncertainties, or plots.

Some earlier version numbers were assigned later. Their dates group related changes and may not match the exact date they became available. For reference datasets and details of the numerical checks, see Numerical validation.

2.9.2 — September 25, 2026

Walkthrough and Help

• The walkthrough highlights the Absolute/Nominal control and reflects the current layout and behavior.
• Model Evaluator messages such as "Enter an x value." now appear beside its heading instead of moving the panel.
• Plot Labels & Axes and Model Evaluator use matching, slightly tighter heading spacing.
• The Absolute/Nominal information icon now sits before the buttons.
• Help now matches recent changes. The Absolute/Nominal choice stays when you change models, the − and + buttons sit beside the model selector, and Calculate sits beside the Model Evaluator heading. Help also lists more fitting software defaults.

Fit calculations and exports are unchanged.

2.9.1 — September 24, 2026

Compact fitting controls

• Model selection and custom parameter controls share the Model heading row, leaving a full-width equation area below.
• Absolute and Nominal sit beside the Uncertainties heading, with their explanation available from the information icon.
• Calculate sits beside the Model Evaluator heading, with wider input and output fields below.
• Setup and saved-fit panels use the same compact layout, with a little more vertical spacing.
• Custom Function shows only − and + beside the model selector, and switching to or from it no longer shifts the controls.
• Absolute or Nominal stays selected when you change models.
• The Absolute/Nominal explanation covers what each choice means, what it changes and other software's defaults, and fits without scrolling.
• The workspace is ready sooner on slow connections: third-party scripts now load after the page finishes.

Fit calculations, uncertainty conventions and exports are unchanged.

2.9.0 — September 23, 2026

Weighted Mean and Parameter Uncertainties

• Weighted Mean combines measurements in y using the supplied δy uncertainties (y = μ), with a plot, residuals, Browser Report and PDF exports. It supports a single measurement.
• The Uncertainties panel offers Nominal and Absolute. Every model defaults to Nominal, including Weighted Mean. Select Absolute for the usual propagated uncertainty of a weighted average. Saved results and PDF footnotes record the convention.
• Expanded Help explains weighting, parameter uncertainties, confidence bands and the Model Evaluator.

Calculation notes: Absolute retains the unscaled parameter covariance; Nominal retains the previous residual-variance scaling. This choice changes uncertainties and confidence bands, not fitted values or goodness of fit. Model uncertainty bands use Student-t coverage for residual-estimated scale and normal coverage for supplied scale. When there are no residual degrees of freedom, residual-scaled fits now report unavailable parameter and propagated uncertainties instead of zero; a one-point mean can still report its supplied uncertainty.

Custom and finite-difference fits using only x uncertainties now use a uniform positive artificial y uncertainty, as analytic built-ins already did. This avoids failed or degenerate fits when a y value is zero and can change x-only results. Previously saved compatible solutions are reused without refitting.

2.8.4 — September 19, 2026

Current labels in Browser Report

• Browser Report uses the current saved-fit title, labels and display scales for its image and PDF downloads. Previously opened reports keep the settings captured when opened.
• Fit Revision links open the requested Results tab instead of Setup.
• Export notices stay compact without shifting the Results panel. Details provides the full explanation and next steps.
• Unavailable exports and label errors give more specific guidance.

Fit calculations, parameter uncertainties and saved scientific inputs are unchanged.

2.8.3 — September 19, 2026

Updated guided practice

• The walkthrough follows the current Results, Export and Browser Report controls, including where to find fit counts and CSV/JSON downloads.
• Custom-equation lessons explain automatic parameters, equation feedback and choosing Keep Custom when a built-in model is suggested.

Fit calculations are unchanged.

2.8.2 — September 2026

Stylesheet loading correction

• Fixed a stylesheet-loading error that could disrupt the layout in Chrome and other browsers without a cached copy.

Fitted values, uncertainties and PDF contents are unchanged.

2.8.1 — September 2026

Clearer export controls

• Export groups larger Single PDF, Double PDF and Browser Report buttons at the bottom of each saved fit.
• Tabs and buttons share uppercase lettering; fit tabs include the date and time. Numerical values retain their formatting.
• Setup and saved-fit action panels align. Panels use white backgrounds, unavailable evaluator values stay blank, and warning details appear on hover or focus.
• Larger loading indicators and disabled export controls make pending work clearer and prevent repeated clicks.
• The Python template is now a minimal runnable example with sample data and a plot. Help explains the available exports.

Fitted values, uncertainties and PDF contents are unchanged.

2.8.0 — September 2026

Help with custom equations

• Catch common equation errors as you type, with suggested corrections you choose whether to apply.
• Parentheses are paired as you type to help you close them correctly.
• Use pi or π in your equation. When you enter a rounded approximation, you can choose to replace it with the constant.
• Switch to a matching built-in model with your parameters mapped to the corresponding controls, or keep your custom equation. Undo lets you reverse the switch.

Calculation note: Existing equation calculations are unchanged. Applying an equation correction changes the input; switching to a built-in model can change the starting estimates and fitting behavior.

2.7.1 — September 2026

More reliable session copying and report links

These changes reached users in 2.8.0; 2.7.1 was not released separately.

• Fork works again, so you can make a separate working copy of a session. Your unsubmitted data and settings survive a reload until the new session saves its first fit.
• The address bar shows the correct session link after Reset, Fork, or opening an example dataset. The session identifier remains readable when highlighted.
• Open a saved fit's browser report with the clearly labeled Detailed Report action.
• Blank or whitespace-only session names are no longer accepted.

Fitted values and PDF plots are unchanged.

2.7.0 — September 2026

A complete report in your browser

• Open a saved fit in a browser report with the fit and residual plots together, full-precision data tables, and the Model Evaluator.
• Review the report without downloading a file, or download its data and results as CSV or JSON.

Fitted values and PDF plots are unchanged.

2.6.1 — September 2026

Open the exact saved fit from a PDF

• Newly generated PDF reports include a direct link to the fit that produced them, as well as the session link.

Fitted values and plots are unchanged.

2.6.0 — September 2026

Six additional fitting models

• Fit with Shifted Reciprocal, Saturation (Michaelis–Menten), Power Law with Vertical Offset, X Log X, Hill Sigmoid (4 Parameter), and Malus’s Law, without entering a custom equation. The new models include automatic starting estimates.
• Exponential is now named Exponential with Offset to make its added constant clearer.
• Malus’s Law expects angles in radians.

Existing models keep the same calculations and starting-value rules.

2.5.0 — September 2026

Clearer plots and equation feedback

• See more detail in model curves and confidence bands. The Setup preview shows all entered observations.
• Paste common mathematical symbols into custom equations and get clearer feedback about missing parameters and unsupported names.
• Saved-fit numbering, undoing a file import, and recovering an export work more reliably. Keyboard navigation and access to the equation field are improved.
• The Setup tab stays blue even when another tab is selected.

Fitted parameters, existing valid custom-equation calculations, and PDF curve sampling are unchanged.

2.4.1 — September 2026

Consistent layout and corrected PDF exports

• The desktop panel arrangement stays consistent on narrower screens. Below 1440 pixels, scroll horizontally to reach the remaining controls.
• PDF export works after changing a completed fit's title, axis labels, or display scales, including in guided practice.

2.4.0 — September 2026

Edit reports without rerunning a fit

• Change a completed fit's title, axis labels, and linear or logarithmic display scales without fitting again. PDF exports use the settings you select.
• Report edits stay with each fit while the page is open. Edits to the newest fit also carry into Setup unless you have already changed that field there. Reloading restores the original saved report settings.
• Try the optional Walkthrough with sample data, fitting, residuals, model evaluation, and exports. Practice opens in a separate tab and leaves your own work untouched.
• Read data on the left and work with plots and fitting controls on the right. Larger text, clearer table shading, and more consistent tabs and controls improve readability. Switching between saved fits is faster.
• Each saved fit keeps its original data even when you edit, cut, or undo changes in Setup. Residual plots keep a linear vertical scale and a clear zero line.
• Import files are checked before replacing your data. Limits are 1 MiB per file, 10,000 data rows, and 256 characters per cell. Slow exports can be rechecked, and export problems have clearer messages.
• Invalid report labels no longer stop an in-page fit; you are asked to correct them when exporting. Repeated PDF exports are faster, and the Model Evaluator no longer fails in certain otherwise valid cases.
• Custom-equation messages distinguish writing errors from calculation problems such as division by zero.

Export change: The Plot PNG button is removed. Existing PNG links still work; Single PDF, Double PDF, Data & Fit CSV, and Fit JSON remain available.

Calculation note: Numeric input now retains its original precision, so high-precision datasets may give different fitted values or uncertainties. Decimal-comma uncertainty input is also handled more consistently. The updated confidence-band calculation for built-in models can slightly change the band, but does not itself change fitted parameters or their uncertainties. Model Evaluator rounding may differ.

2.3.2 — September 2026

Improved fitting accuracy and clearer uncertainty warnings

These changes reached users in 2.4.0; 2.3.2 was not released separately.

• Fits are checked more closely before they are considered finished. The included NIST reference cases show improved agreement in fitted parameters and uncertainties, including when using their published starting values.
• Fits can identify additional cases where the data cannot determine reliable parameter uncertainties, including a difficult narrow-peak example.
• Long-running fits report timeouts more reliably, without extending the existing calculation time limit.

Calculation note: Fitted values, uncertainties, and warnings can change for any model or uncertainty setting. A small residual score alone does not establish that every parameter is accurately determined.

2.3.1 — September 2026

Browse your full fit history

These changes reached users in 2.4.0; 2.3.1 was not released separately.

• Find every earlier fit in Previous, using Newer and Older to move through long histories. Fit numbers stay consistent, and already-open fits are labeled.
• Fits with warnings are easier to spot. Reduced chi-squared uses the same highlighting in the workspace and reports.
• Reset and Fork work reliably again. Reset clears the workspace; Fork starts a separate session from the selected fit.

Removed: The old Raw Data output and its previously saved links no longer open. Other saved fit links and the existing PDF, PNG, CSV, and JSON outputs remain available. The Model Evaluator is available in the fit panel.

Fit calculations are unchanged from 2.2.8. The documented comparison found identical results for all fourteen reference cases in both fitting modes.

2.3.0 — September 2026

Fit results directly in the workspace

These changes were included in the intermediate 2.3.1 update and reached users in 2.4.0; 2.3.0 was not released separately.

• Press Fit! to see your result in a tab beside Setup, with the plot, equation, parameter values and uncertainties, fit statistics, and warnings. The three most recent fits stay open; earlier fits are available through Previous.
• Each fit shows the data it used, its fitted curve and 68.27% confidence band, and a switch between the fit and residual plots. Saved-fit data are read-only; later edits in Setup do not change earlier results.
• Use the Model Evaluator to calculate a model value and its uncertainty at an x value you choose.
• Choose exports after fitting rather than before: Single PDF, Double PDF, Plot PNG, Data & Fit CSV, and Fit JSON. Files are prepared when requested.
• Reopen a session in another browser with its most recent data and three latest fits, keeping their original fit numbers.
• Custom parameter buttons work again, blank rows before your data are accepted, and Reset clears logarithmic display settings correctly. Fit requests start faster, with a countdown when you need to wait before fitting again.
• Plot size and positioning stay consistent between tabs. Axis labels remain in Setup and downloaded reports rather than on the in-page fit plot.

Removed: Raw Data is no longer offered as an output choice. Its saved links were also retired in 2.3.1.

Fit calculations are unchanged from 2.2.8. The documented comparison found identical results for all fourteen reference cases in both fitting modes.

2.2.8 — September 2026

Help and template buttons work again

• TEMPLATE and HELP respond to clicks again; the feedback control no longer blocks them.

Fit calculations are unchanged.

2.2.7 — September 2026

Compare a fully specified model with your data

• Hold every parameter fixed to plot the model exactly as entered. Results include residuals and fit statistics, with a clear “All parameters fixed: model plotted, not fitted” notice. Parameter uncertainties are shown as zero and no confidence band is displayed.
• Corrected overstated uncertainties in some fits with fixed parameters. Fits with no fixed parameters are unaffected.
• Press Enter while Fit! is focused to start a fit. Help includes screen-size guidance, and the feedback button is easier to use.
• Expanded checks of fitting behavior and uncertainty estimates; see Numerical validation.

Calculation note: Fitted parameter values are unchanged. Uncertainties can change only in the affected fixed-parameter cases; fully fixed models now produce a defined result.

Which fixed-parameter results are affected?

The correction applies when at least one parameter is fixed and a data point has zero sensitivity to every free parameter. Examples include x = 0 with a fixed intercept, or points far from a Gaussian peak with a fixed offset. Uncertainty scaling now uses the number of observations minus the number of free parameters.

2.2.6 — September 2026

Fewer misleading fit warnings

• Corrected false “Not full rank” warnings for exact fits and for fits with parameters on very different scales, including the NIST Pontius example.
• Data with constant y values can be fitted. R² is shown as n/a when it is undefined rather than causing the fit to fail.
• Corrected oscillator confidence bands when the displayed phase is adjusted across ±π, and fixed the feedback button's appearance.

Calculation note: Fitted parameter values and their uncertainties are unchanged. Warning messages and R² displays are corrected in the cases above; affected oscillator confidence bands can change.

2.2.5 — September 2026

Easier file import and feedback

• Import comma-, tab-, or semicolon-separated data, skip blank lines, and import the same file again when needed. A file with no numeric rows now produces a clear message.
• Find FEEDBACK beside TEMPLATE and HELP during the feedback period.

Fit calculations and file-column mapping are unchanged.

2.2.4 — September 2026

Clearer warnings and corrected uncertainty bands

• Results show all relevant fitting warnings, rather than only the first. A parameter uncertainty that cannot be determined is shown as n/a, not zero. Warnings are also included in JSON downloads.
• Corrected confidence bands and Model Evaluator uncertainties for Gaussian and Lorentzian fits whose width was adjusted from negative to positive for display.

Calculation note: Fitted parameter values and their individual uncertainties are unchanged. Confidence bands and Model Evaluator uncertainties can change in the affected width-correction cases.

2.2.3 — September 2026

More reliable results for very small coefficients

• Corrected fits with extremely small automatically estimated coefficients, including the NIST Pontius example. These cases could previously show an incorrect warning or an uncertainty that was too small.
• Failed calculations now show an explanation instead of returning results containing nan. Input uncertainties must be finite and positive; percentage and proportional uncertainties use the magnitude of the data value.
• Added this changelog, the footer version link, and Help's Numerical validation section.

Calculation note: Fits affected by the very-small-coefficient issue can change; the certified NIST Pontius values are reproduced. Fits that previously returned non-numeric results now fail with an explanation. Other fits are unchanged.

2.2.2 — September 5, 2026

Clearer uncertainty controls

• Shaded δx and δy columns show which uncertainty values are currently unused. You can still edit them; they become active when you select Table for that uncertainty.
• Column shading updates correctly when you switch settings.

Fit calculations are unchanged.

2.2.1 — September 4, 2026

Corrected unexpected zero uncertainties

• Corrected some fits that reported zero uncertainty for a free parameter when its automatic starting estimate was extremely close to zero.
• The fix applies across all four uncertainty settings: none, x only, y only, and both x and y. Starting values are unchanged.

Calculation note: Affected fitted values and uncertainties may change. Recheck earlier fits with unexpectedly zero uncertainty for a free parameter. This does not resolve models that the data cannot adequately constrain. The correction was refined in 2.2.3.

2.2.0 — September 4, 2026

Updated built-in fitting calculations

• Updated calculations for all 19 built-in models, using derivatives obtained directly from their equations.
• Corrected x-only uncertainty handling that could incorrectly show a free parameter as undetermined with zero uncertainty.

Calculation note: Rerunning built-in models can change fitted values, uncertainties, and whether a fit converges. The custom-equation fitting method is unchanged.

Validation results and limitations

The derivatives were checked independently, and built-in models were tested with synthetic data using x-only and combined x/y uncertainties.

For the Gaussian Energy reference case, fitted parameters changed by less than 0.5% and reported uncertainties by less than 4% compared with the previous implementation. Those observations apply to that test case, not to every dataset.

Some Lorentzian, exponential, and other poorly constrained fits can still give unreliable parameter uncertainties. A successful fit or smaller residual does not establish that every parameter is well determined. This release did not yet provide all the warnings for those cases.

2.1.0 — September 1, 2026

More reliable custom-equation fitting

• Some valid custom equations that were previously rejected can now be fitted successfully.
• Plots skip regions where a custom equation is undefined instead of failing the entire result.
• Added a temporary feedback form for reporting issues.

Calculation note: Previously rejected custom fits may now succeed, but results must still be finite and real at the observed data points. Built-in calculations are unchanged.

2.0.0 — August 2026

An updated curve.fit

• Introduced the updated application while retaining the familiar model choices, uncertainty controls, starting and fixed parameters, and the PDF and Raw Data outputs available at the time.
• Pages and plots load more quickly. Reset clears old points and error bars, and Raw Data tables stay within the report page.
• Added NIST Norris, Pontius, Misra1a, Eckerle4, and DanWood datasets, alongside the Pearson–York benchmark and Gaussian examples.

Calculation note: All nine reference cases passed the documented comparison with the previous application within the specified tolerances. This does not guarantee identical results for every dataset.

1.0.0 — Legacy version

The original curve.fit application, before the version 2 transition. Earlier changes are not reconstructed here.