As far as I can recall Microsoft uses a cubic spline but I have not seen the
exact formula.
Try Google with search term: excel spline
best wishes
--
Bernard V Liengme
Microsoft Excel MVP
www.stfx.ca/people/bliengme
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I have some raw data in excel, with a smooth curve added. I am trying
to reproduce this curve on the same data in GraphPad Prism, with poor
results. Does anyone know how excel calculates curve smoothing?