Not sure where the discrepancy arises but the minimum will be somewhat resolution dependent if the line is not fully resolved.
OK so the difference between my measurement and the BASS2000 spectrum is not just due to a difference in resolution. See attached comparison where the BASS2000 spectrum has been spline filtered to ~ match the resolution in my spectrum. The discrepancy is still there and looks to be due to a zero offset so I need to check back on how I did the background subtraction.
