Wayne, > get the spectrum value there. Only for points between 256.5 and 257 (but > < 257) the nearest position is 257, which is outside the grid, so the code > was getting an error because it was not correcting for this. It is now > wrapping around to point 1 instead. Are you taking notice of whether the folding is "aliasing" or "folding" yet? I know the data model has support for both, but last time I looked analysis only handled "aliasing" (which is indeed what most people do). Might that impact on the point sums? Brian