--- loncom/interface/statistics/lonproblemanalysis.pm	2006/01/22 04:10:04	1.123
+++ loncom/interface/statistics/lonproblemanalysis.pm	2006/02/04 19:06:53	1.124
@@ -1,6 +1,6 @@
 # The LearningOnline Network with CAPA
 #
-# $Id: lonproblemanalysis.pm,v 1.123 2006/01/22 04:10:04 bowersj2 Exp $
+# $Id: lonproblemanalysis.pm,v 1.124 2006/02/04 19:06:53 bowersj2 Exp $
 #
 # Copyright Michigan State University Board of Trustees
 #
@@ -401,7 +401,8 @@ sub numerical_plot_differences {
     } elsif ($low_bin < 0 && $high_bin < -$low_bin) {
         $high_bin = -$low_bin;
     }
-    if (($high_bin -$low_bin)/$min_bin_size * 2 > $max_bins) {
+    if (!$min_bin_size ||
+        ($high_bin -$low_bin)/$min_bin_size * 2 > $max_bins) {
         $min_bin_size = abs($high_bin - $low_bin) / $max_bins * 2;
     }
     my @bins;