Trending of comp stars

Posted by ghawkins on Apr 08, 2022; 2:22am
URL: http://astroimagej.170.s1.nabble.com/Trending-of-comp-stars-tp1874.html

If I have two comp stars and I'm looking at their normalized relative flux plots, and one trends up and the other trends down with a similar but opposite slope, then am I correct in saying that some unknown systematic (likely airmass) is affecting the comp stars in different ways?  If the unknown systematic was affecting the comp stars in the same way, then the normalized relative flux plots for each comp star would be flat.