  We describe the recent modifications to the data reduction technique for
observations acquired with the scanning Fabry-Perot interferometer (FPI)
mounted on the 6-m telescope of the Special Astrophysical Observatory that
allow the wavelength scale to be correctly computed in the case of large mutual
offsets of studied objects in interferograms. Also the parameters of the
scanning FPIs used in the SCORPIO-2 multimode focal reducer are considered.
