Index: trunk/ppStack/src/ppStackSources.c
===================================================================
--- trunk/ppStack/src/ppStackSources.c	(revision 21016)
+++ trunk/ppStack/src/ppStackSources.c	(revision 21092)
@@ -10,9 +10,9 @@
 
 
-bool ppStackSourcesTransparency(const psArray *sourceLists, const pmFPAview *view, const pmConfig *config)
+float ppStackSourcesTransparency(const psArray *sourceLists, const pmFPAview *view, const pmConfig *config)
 {
-    PS_ASSERT_ARRAY_NON_NULL(sourceLists, false);
-    PS_ASSERT_PTR_NON_NULL(view, false);
-    PS_ASSERT_PTR_NON_NULL(config, false);
+    PS_ASSERT_ARRAY_NON_NULL(sourceLists, NAN);
+    PS_ASSERT_PTR_NON_NULL(view, NAN);
+    PS_ASSERT_PTR_NON_NULL(config, NAN);
 
 #ifdef TESTING
@@ -46,5 +46,5 @@
     if (!airmassZP) {
         psError(PS_ERR_UNKNOWN, false, "Unable to find ZP.AIRMASS in recipe.");
-        return false;
+        return NAN;
     }
 
@@ -69,5 +69,5 @@
                     exptime, airmass, expFilter);
             psFree(zp);
-            return false;
+            return NAN;
         }
 
@@ -79,10 +79,10 @@
                         "Unable to find airmass term (ZP.AIRMASS) for filter %s", filter);
                 psFree(zp);
-                return false;
+                return NAN;
             }
         } else if (strcmp(filter, expFilter) != 0) {
             psError(PS_ERR_BAD_PARAMETER_VALUE, false, "Filters don't match: %s vs %s", filter, expFilter);
             psFree(zp);
-            return false;
+            return NAN;
         }
 
@@ -95,5 +95,5 @@
         psError(PS_ERR_UNKNOWN, false, "Unable to match sources");
         psFree(zp);
-        return false;
+        return NAN;
     }
     psVector *trans = pmSourceMatchRelphot(matches, zp, iter, tol, starLimit, transIter, transRej,
@@ -128,5 +128,5 @@
     if (!trans) {
         psError(PS_ERR_UNKNOWN, false, "Unable to measure transparencies");
-        return false;
+        return NAN;
     }
 
@@ -158,5 +158,5 @@
             psError(PS_ERR_UNKNOWN, false, "Unable to match sources");
             psFree(zp);
-            return false;
+            return NAN;
         }
         psVector *trans = pmSourceMatchRelphot(matches, zp, iter, tol, starLimit, transIter, transRej,
@@ -165,4 +165,5 @@
     }
 #endif
-    return true;
+
+    return sumExpTime;
 }