What to put in the offset files:
       offset_file:       to combine all 4 files (with 2 different wavlengths):
       0 69               0 69
       0 0                0 0
                          37.5 69
			  37.5 0

To determine the y offset look in the headers, the offset will be the following:
    - (NODBYOFF - NODAYOFF) / PIXSCALE

To determine x offset:
    - difference in central wavelength in angstroms / PIXSCALE