WP: The FitSEries can also calculate R?Yes. Look at TFitSeries.FitStatistics (https://wiki.lazarus.freepascal.org/TAChart_documentation#Fit_series).
When the fit equation is (for example R2 = 0.93) how can I put R2 on the line? or how can I show itWhich "line"? TFitSeries only provides the value, you can choose any way to display it (in the Chart.Foot, in a label, in a MessageBox, in a memo, ...) The fitdemo project in (lazarus)/components/tachart/demo/fit is rather versatile. (After having put some work into LazStats (https://sourceforge.net/p/lazarus-ccr/svn/HEAD/tree/applications/lazstats/) I have some doubt whether the calculation of the confidence levels in TAChart is correct.).