Index: trunk/ppStack/src/ppStackConvolve.c
===================================================================
--- trunk/ppStack/src/ppStackConvolve.c	(revision 31158)
+++ trunk/ppStack/src/ppStackConvolve.c	(revision 32170)
@@ -377,5 +377,6 @@
             0.5 * (values->data.F32[numGood / 2 - 1] + values->data.F32[numGood / 2]);
 
-        float rms = 0.74 * (values->data.F32[numGood * 3 / 4] -
+	// EAM/MEH ensure RMS is positive
+        float rms = 0.74 * fabsf(values->data.F32[numGood * 3 / 4] -
                             values->data.F32[numGood / 4]); // Estimated RMS from interquartile range
         psFree(values);