Index: trunk/MagicSoft/Mars/manalysis/MHillas.cc
===================================================================
--- trunk/MagicSoft/Mars/manalysis/MHillas.cc	(revision 1350)
+++ trunk/MagicSoft/Mars/manalysis/MHillas.cc	(revision 1353)
@@ -281,7 +281,7 @@
     // -------------------------------------------------------------------
     //
-    const float d = corryy - corrxx;
-
-    fDelta = atan2(d + sqrt(d*d + corrxy*corrxy*4), corrxy*2);
+    const float d = (corryy - corrxx)/(corrxy*2);
+
+    fDelta = atan(d + sqrt(d*d + 1));
 
     fCosDelta = cos(fDelta);   // need these in derived classes