Index: /trunk/MagicSoft/Mars/mhist/MHCurrents.cc
===================================================================
--- /trunk/MagicSoft/Mars/mhist/MHCurrents.cc	(revision 2190)
+++ /trunk/MagicSoft/Mars/mhist/MHCurrents.cc	(revision 2191)
@@ -146,4 +146,5 @@
         fSum[idx] += val;
         fRms[idx] += val*val;
+
     }
 
@@ -171,5 +172,13 @@
         fRms[i] -= fSum[i]*fSum[i]/fEntries;
         fRms[i] /= fEntries-1;
-        fRms[i]  = TMath::Sqrt(fRms[i]);
+
+        if (fRms[i]<0)
+        {
+            *fLog << warn << "WARNING - fRms[" << i <<"]= " << fRms[i] << " -> was set to 0 " << endl;
+            fRms[i]=0;
+        }
+
+        else
+            fRms[i]  = TMath::Sqrt(fRms[i]);
 
         // calc mean value for pixel index i