Some functions (e.g. the Rayleigh function for small-angle scattering from spheres) expect Q as the independent variable. You can use these models even if you have plotted data versus 2theta or Q2 by checking the "Use Q as Fit Variable" box. This will be true for all submodels used, even those such as Gaussian which do not necessarily require Q as the independent parameter. Do not check this box if you want to be sure that the variable you used for plots to be that used for the fit itself. If Datasqueeze thinks you might have made a mistake in selecting (or not selecting) this box, an dialog box pops up at the point when you actually perform the fit. |