What to put in the offset files:
offset_file: to combine all 4 files (with 2 different wavelengths): 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