I have two questions: I have a set of data, a measured spectrum. When I model the spectrum with a function, I calculate r2=1-([itex]\sum[/itex](y-ymodel)2/[itex]\sum[/itex](y-yavg)2). Q1) However, I have reference data now, which is what the spectrum should be. So is it right to use the same calculation on it for r2, but instead of using ymodel, using yreference? Q2) The model function I was fitting to the data is Sλ = 2πhc2/λ5(ehc/λkT-1) Is it correct to calculate goodness of fit in that way for such a distribution? Here is a plot of my two data sets thanks!