A simple regression model is fitted to the data.

ch.Set 'style' 'model'

The default is a linear ‘straight-line’ fit but you can use the Order of Fit setting to fit models up to quartics. The line may be annotated with the regression coefficients. If the ‘risers’ style is also set, the risers are drawn from the fitted line:

Fitting 3D data
If the modelfit style is used with the cloud chart, the fit is made against both X and Y axes, and the order of fit may be set independently for either.

Here, the model is quadratic in both X and Y. Contour lines are shown, and risers have been used to show the residual values in the Z-direction.