Least squared method is used for approximation of the spectral data. Curve range sets the frequency interval in which a curve is drawn. The middle part between utmost measurement points has selected curve type. All weights are given equal.
All weights are inverse proportional to the flux errors.
All weights are inverse proportional of the squares to the flux errors. If the frequencies differ less than the quarter of the decade these spectra points can be considered as indistinguishable. The button being switched on, such points are examined as one when you choose the curve type.