SKYLINE searches the night sky spectrum in buffer 's1' for known night sky emission lines. All spectra must be linear wavelength calibrated. If it finds at least two lines in the spectrum it will use them to compute a corrected zero-point for the wavelength scale (the dispersion term is not changed). This new zero-point is then applied to all of the other spectra supplied on the command line. All of the spectra should be on the same linear wavelength scale (using the ALIGN command) to begin with.
If the keyword INT is used then you will be given the option to delete lines from the list of night sky lines found in spectrum 's1'.
MASH is used to operate on image 8, producing a sky-subtracted program spectrum in buffer 1 and the sky spectrum in buffer 2. Wavelength parameters are copied from a previously calibrated comparison spectrum (in buffer 20). The two spectra are transformed to a linear wavelength scale using ALIGN. Then the zero-point of the wavelength scale is corrected using SKYLINE. This procedure can remove instrumental flexure if your spectra contain usable night-sky lines.