Index: /trunk/Ohana/src/uniphot/src/cam_zpt_correction.c
===================================================================
--- /trunk/Ohana/src/uniphot/src/cam_zpt_correction.c	(revision 39277)
+++ /trunk/Ohana/src/uniphot/src/cam_zpt_correction.c	(revision 39278)
@@ -385,5 +385,8 @@
 	float delta = FlatCorrectionOffset (flatcorr, ID, chipX, chipY);
 
-	values[jx + jy*NxModel] += delta;
+	// note that Eddie's offset is defined so that Mrel = Mcat + offset
+	// while my flatfield dM is defined so that dM = Mcat - Mrel or Mrel = Mcal - dM
+	// note that in the old code, measure.Mcal = -offset and Mrel = Mcat - Mcal
+	values[jx + jy*NxModel] -= delta;
       }
     }