A basic technique in statistics is "regression", which just means fitting a curve (or surface) to data points. This has been studied extensively for 200 years since Gauss invented least squares. Statisticians have very precise measures of how well a curve fits the data. (E.g., "A Second Course in Statistics: Regression Analysis" (7th Edition) by Mendenhall and Sincich.) —Dan Henry Baker wrote: ----- Should statistics & spreadsheet programs utilize such a method to warn users that the fit they've chosen isn't very good? -----