Index: trunk/psModules/src/imcombine/pmStack.c
===================================================================
--- trunk/psModules/src/imcombine/pmStack.c	(revision 31721)
+++ trunk/psModules/src/imcombine/pmStack.c	(revision 34150)
@@ -357,5 +357,6 @@
         sumWeight += weights->data.F32[i];
         if (variances) {
-            sumVarianceWeight += variances->data.F32[i] * PS_SQR(weights->data.F32[i]);
+	  //            sumVarianceWeight += variances->data.F32[i] * PS_SQR(weights->data.F32[i]);
+	  sumVarianceWeight += 1 / variances->data.F32[i];
         }
         if (exps) {
@@ -372,5 +373,6 @@
     *mean = sumValueWeight / sumWeight;
     if (var) {
-        *var = sumVarianceWeight / PS_SQR(sumWeight);
+      //*var = sumVarianceWeight / PS_SQR(sumWeight);
+      *var = 1 / sumVarianceWeight;
     }
     if (exp) {