I lied. Chris Elledge also asked about fixed exposure flats. I gave him the same info. I suspect this is a recipe out of the past or driven by some limitation of software (not ACP ha ha). Maybe I am wrong as I said I am no expert! I await Eric Dose and/or Dick Berg and/or ???. If needed I will reach out to Arne Henden, former USNO, former Director of AAVSO , and designer of the APASS Project (which is being done with ACP Expert).