Index: trunk/ppStack/src/ppStackSources.c
===================================================================
--- trunk/ppStack/src/ppStackSources.c	(revision 20995)
+++ trunk/ppStack/src/ppStackSources.c	(revision 21016)
@@ -87,5 +87,5 @@
         }
 
-        zp->data.F32[i] = airmassTerm * airmass + 2.5 * log10(exptime);
+        zp->data.F32[i] = airmassTerm * airmass - 2.5 * log10(exptime);
         sumExpTime += exptime;
     }
@@ -131,5 +131,5 @@
     }
 
-    // M = m + c0 + c1 * airmass + 2.5log(t) + transparency
+    // M = m + c0 + c1 * airmass - 2.5log(t) + transparency
     // Want sources to have m corresponding to airmass = 1 and t = sumExpTime and transparency = 0
     // m_0 + c1 * airmass_0 + 2.5log(t_0) - trans_0 = m_1 + c1 * airmass_1 + 2.5log(t_1) - trans_1
@@ -138,5 +138,5 @@
     for (int i = 0; i < num; i++) {
         psArray *sources = sourceLists->data[i]; // Sources of interest
-        float magCorr = airmassTerm + 2.5*log10(sumExpTime) - zp->data.F32[i] - trans->data.F32[i];
+        float magCorr = airmassTerm - 2.5*log10(sumExpTime) - zp->data.F32[i] - trans->data.F32[i];
         psLogMsg("ppStack", PS_LOG_INFO, "Applying magnitude correction to image %d: %f\n", i, magCorr);
 
@@ -150,5 +150,4 @@
     }
     psFree(trans);
-
 
 #ifdef TESTING