The following calibration format can be used directly in IRAF.digiphot.photcal.invertfit. The instrumental magnitudes mU, mB, and mV are -2.5*log(counts/s)+25. For the these images, the average parameters for UBV are the following: Airmass---1.65, 1.65, 1.68 Integration time (s)---600, 500, 200 Pixel scale (arcsec)---0.27, 0.27, 0.27 begin UFIT status 0 parameters 2 u1 u2 derivatives 2 0.1 0.1 values 2 2.197749 -0.128126 errors 2 0.003785 0.009613 begin BFIT status 0 parameters 2 b1 b2 derivatives 2 0.1 0.1 values 2 0.0482687 -0.05287 errors 2 0.02294 0.0282 begin VFIT status 0 parameters 2 v1 v2 derivatives 2 0.1 0.1 values 2 -0.117043 0.06056194 errors 2 0.00857 0.0106