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---1.043, 1.038, 1.037 Integration time (s)---200, 30, 30 Pixel scale (arcsec)---0.43, 0.43, 0.43 begin UFIT status 0 parameters 2 u1 u2 derivatives 2 0.1 0.1 values 2 3.18883 -0.197586 errors 2 0.007 0.012 begin BFIT status 0 parameters 2 b1 b2 derivatives 2 0.1 0.1 values 2 0.4841993 0.0337471 errors 2 0.0105 0.01272 begin VFIT status 0 parameters 2 v1 v2 derivatives 2 0.1 0.1 values 2 -0.1803645 -0.0204284 errors 2 0.008 0.009