If you fix a line wavelength outside your plot, it will NOT be taken into account. Wrong baseline . If you fit a baseline without selecting baseline parts, the whole spectra is used which may give unusable baseline for faint lines. It is not possible for the moment to fit correctly nor simply a faint line merged with noise or fringes. Baseline fit is constant.
Baseline fit is linear.
Baseline fit is a 2 degree polynomial. Baseline fit is a 3 degree polynomial. For non-composite fits, these parameters are set to zero. Note that this method does not allow the baseline fit and line fit together as in Gaussian method. Wavelengths are fitted if 0, or outside plot window current range.