Hi Joseph, The Fourier transform parameters for the background subtraction do not need to be the same for the analysis of chi(k). In fact, they really shouldn't be the same -- the goals for these FTs are very different., as the FT for background subtraction is only to determine a good background function and to identify the oscillations in chi(k), not to analyze them. Setting the k-weighting to 3 for the background subtraction effectively tells the program to not care about the background at low k. This can cause wild oscillations in the background at both low- and high-k, especially when using clamps of any kind. For background subtraction, the k-weight should be 1, though using 2 and sometimes 0 also work well in many situations. Furthermore kmin should be very close to 0 (1 Ang^-1, at the most, though there may be special situations), which is usually too low for most analysis of chi(k). Hope that helps, --Matt