Workspace
The main window is CFTool’s central workspace — it shows your data, fits and results, and gives quick access to fit-quality and diagnostic information.
01Layout overview
The window is divided into four panels:
- Main graph — plots your data, fits, and any additional lines or functions.
- Residuals plot — appears below the main graph.
- Results panel — to the right of the main graph.
- Feedback panel — below the results panel.
02The Line Selector
CFTool works on one line at a time, chosen with the Line Selector drop-down (below the control ribbon):
- Primary Line — your first dataset and its fit.
- Secondary Line — the second dataset and its own fit; shown as Function Line when Function Mode is on.
- Full Graph — both lines displayed together. This is a view: line-specific controls (fit type, limits, single-line label editing, the Extend Fit button) are locked — switch back to a single line to change it.
Whichever line is selected is the one the fit controls, limits, results and Label Editor act on. See Plotting a second line for the full workflow.
03Residuals plot
The residuals plot shows how each data point deviates from the fitted curve.
- If your model is correct, the residuals should resemble random Gaussian noise scattered evenly around zero.
- If they show a pattern or structure, your model may be incomplete or physically inappropriate.
Two buttons control it:
- Hide Residuals — hides the residuals panel to enlarge the main graph area.
- Show Histogram — opens a separate window with a histogram of the residuals, to help visualise their distribution.
How to read the residuals plot.
- Random scatter around zero → the model is probably suitable.
- Curvature or waves → the model may be missing a term (e.g. quadratic or sinusoidal behaviour).
- Systematic offset → a constant term or background may be missing.
- Clusters or asymmetry → the σ values may be mis-estimated, or the weighting may need review.
Randomness is usually a good sign; structure or bias means the fit can be improved.
04Results panel
The Results panel, to the right of the main plot, lists:
- The best-fit coefficient values.
- The confidence intervals (errors) for each coefficient.
- The fit limits used for the analysis.
- The definite integral of the fit between those limits.
These values update automatically each time a fit is performed.
05Fit-quality indicators
Below the coefficient table, several numerical indicators help you assess the fit:
- SSE (Sum of Squares of Errors) — the sum of the squared differences between the data and the fitted model. Smaller values indicate a better numerical match.
- R² (Coefficient of Determination) — measures how well the model reproduces the variation in the data. Values close to 1.0 indicate an excellent fit; values near 0 a poor one.
R² is not proof. High SSE or low R² indicate a poor match, but even a high R² does not confirm that the chosen function is physically valid — it only shows that it reproduces the shape of the data well.
06Feedback panel
The text panel beneath the Results section provides messages, warnings and feedback. It reports:
- Problems encountered during fitting.
- Issues with custom functions (e.g. syntax or undefined parameters).
- Other messages relevant to particular fitting tools.
If a fit fails or produces unexpected results, check this panel first — it usually indicates what went wrong.
