software for difference spectra?

[Dan Strahs]

	I'm looking for software to construct difference spectra.  I would 
like it to be X-based platform and be compatible with Unix (Silicon Graphics'
IRIX, to be exact).  

	I need to subtract graphs/spectra of molecule with and without ligand
in order to accurately quantitate conformational changes.  The graphs/spectra
are only approximately on the same scale and I need to be able to align the
spectra using common features.

	Thanks,
		Dan Strahs