Index: trunk/ppSim/src/ppSimMakeBias.c
===================================================================
--- trunk/ppSim/src/ppSimMakeBias.c	(revision 14657)
+++ trunk/ppSim/src/ppSimMakeBias.c	(revision 14667)
@@ -46,6 +46,6 @@
 
 	    // Bias level
-	    signal->data.F32[y][x] = biasRows->data.F32[y];
-	    variance->data.F32[y][x] = PS_SQR(readnoise);
+	    signal->data.F32[y][x] += biasRows->data.F32[y];
+	    variance->data.F32[y][x] += PS_SQR(readnoise);
 
 	}