WSCALE calculates the wavelength calibration polynomial using the wavelengths and line centers of the calibration spectrum lines identified by the LINEID command. The resulting calibration is associated with the spectrum specified by 'dest'. The line centers determined with the LINEID command are fit to a polynomial of order specified by 'ORD=n'. If the keyword 'INT' is specified, interactive line weighting can be done. The program will ask for all unspecified parameters.
The resulting wavelength scale becomes associated with the 'dest' spectrum. You can then use the COPW command to associate the wavelength scale with any other spectrum you wish.
Also, note that it is the REVERSE fit which is actually used by the command ALIGN to linearize a spectrum (see below).