Index: trunk/psModules/src/objects/pmSourceMoments.c
===================================================================
--- trunk/psModules/src/objects/pmSourceMoments.c	(revision 38872)
+++ trunk/psModules/src/objects/pmSourceMoments.c	(revision 38873)
@@ -409,4 +409,6 @@
 	    float yy = yDiff * y;
 
+	    // the factor of 1/r makes these appropriate for measuring
+	    // \sum r^2 cos(3 theta), sin(3 theta) (psphotImageQuality.c:107)
 	    float xxx = xDiff * xx / r;
 	    float xxy = xDiff * xy / r;
@@ -414,4 +416,6 @@
 	    float yyy = yDiff * yy / r;
 
+	    // the factor of 1/r^2 makes these appropriate for measuring
+	    // \sum r^2 cos(4 theta), sin(4 theta) (psphotImageQuality.c:107)
 	    float xxxx = xDiff * xxx / r2;
 	    float xxxy = xDiff * xxy / r2;
Index: trunk/psphot/src/psphotImageQuality.c
===================================================================
--- trunk/psphot/src/psphotImageQuality.c	(revision 38872)
+++ trunk/psphot/src/psphotImageQuality.c	(revision 38873)
@@ -98,9 +98,12 @@
         // r^2 sin(2t) = r^2 2 cos t sin t = 2 x y
 
-        // r^3 cos(3t) = r^3 cos^3 t - r^2 3 cos t sin^2 t = (x^3 - 3 x y^2)
-        // r^3 sin(3t) = r^3 3 cos^2 t sin t - sin^3 t = (3 x^2 y - y^3)
-
-        // r^4 cos(4t) = r^4 cos^4 t - r^2 6 cos^2 t sin^2 t + r^2 sin^4 t = (x^4 - 6 x^2 y^2 + y^4)
-        // r^4 sin(4t) = r^4 4 cos^3 t sin t - 4 sin^3 t cos t = (4 x^3 y - 4 y^3 x)
+        // r^2 cos(3t) = r^2 cos^3 t - r^2 3 cos t sin^2 t = (x^3 - 3 x y^2) / r
+        // r^2 sin(3t) = r^2 3 cos^2 t sin t - sin^3 t = (3 x^2 y - y^3) / r
+
+        // r^2 cos(4t) = r^2 cos^4 t - r^2 6 cos^2 t sin^2 t + r^2 sin^4 t = (x^4 - 6 x^2 y^2 + y^4) / r^2
+        // r^2 sin(4t) = r^2 4 cos^3 t sin t - 4 sin^3 t cos t = (4 x^3 y - 4 y^3 x) / r^2
+
+	// NOTE that Mxxx,etc have the factor of r in the denominator, while Mxxxx,etc have the factor of r^2.
+	// See pmSourceMoments.c:418
 
         num++;