Index: /trunk/psModules/src/objects/models/pmModel_GAUSS.c
===================================================================
--- /trunk/psModules/src/objects/models/pmModel_GAUSS.c	(revision 10077)
+++ /trunk/psModules/src/objects/models/pmModel_GAUSS.c	(revision 10078)
@@ -49,6 +49,7 @@
         dPAR[PM_PAR_XPOS] = q*(2*px/PAR[PM_PAR_SXX] + Y*PAR[PM_PAR_SXY]);
         dPAR[PM_PAR_YPOS] = q*(2*py/PAR[PM_PAR_SYY] + X*PAR[PM_PAR_SXY]);
-        dPAR[PM_PAR_SXX]  = +2.0*q*px*px/PAR[PM_PAR_SXX];
-        dPAR[PM_PAR_SYY]  = +2.0*q*py*py/PAR[PM_PAR_SYY];
+        // the extra factor of 2 below is needed to avoid excessive swings
+        dPAR[PM_PAR_SXX]  = +4.0*q*px*px/PAR[PM_PAR_SXX];
+        dPAR[PM_PAR_SYY]  = +4.0*q*py*py/PAR[PM_PAR_SYY];
         dPAR[PM_PAR_SXY]  = -q*X*Y;
     }
Index: /trunk/psModules/src/objects/models/pmModel_PGAUSS.c
===================================================================
--- /trunk/psModules/src/objects/models/pmModel_PGAUSS.c	(revision 10077)
+++ /trunk/psModules/src/objects/models/pmModel_PGAUSS.c	(revision 10078)
@@ -50,6 +50,7 @@
         dPAR[PM_PAR_XPOS] = q*(2.0*px/PAR[PM_PAR_SXX] + Y*PAR[PM_PAR_SXY]);
         dPAR[PM_PAR_YPOS] = q*(2.0*py/PAR[PM_PAR_SYY] + X*PAR[PM_PAR_SXY]);
-        dPAR[PM_PAR_SXX] =  +2.0*q*px*px/PAR[PM_PAR_SXX];
-        dPAR[PM_PAR_SYY] =  +2.0*q*py*py/PAR[PM_PAR_SYY];
+        // the extra factor of 2 below is needed to avoid excessive swings
+        dPAR[PM_PAR_SXX] =  +4.0*q*px*px/PAR[PM_PAR_SXX];
+        dPAR[PM_PAR_SYY] =  +4.0*q*py*py/PAR[PM_PAR_SYY];
         dPAR[PM_PAR_SXY] = -q*X*Y;
     }
Index: /trunk/psModules/src/objects/models/pmModel_QGAUSS.c
===================================================================
--- /trunk/psModules/src/objects/models/pmModel_QGAUSS.c	(revision 10077)
+++ /trunk/psModules/src/objects/models/pmModel_QGAUSS.c	(revision 10078)
@@ -63,6 +63,7 @@
         dPAR[PM_PAR_XPOS] = q*(2.0*px/PAR[PM_PAR_SXX] + Y*PAR[PM_PAR_SXY]);
         dPAR[PM_PAR_YPOS] = q*(2.0*py/PAR[PM_PAR_SYY] + X*PAR[PM_PAR_SXY]);
-        dPAR[PM_PAR_SXX]  = +2.0*q*px*px/PAR[PM_PAR_SXX];
-        dPAR[PM_PAR_SYY]  = +2.0*q*py*py/PAR[PM_PAR_SYY];
+        // the extra factor of 2 below is needed to avoid excessive swings
+        dPAR[PM_PAR_SXX]  = +4.0*q*px*px/PAR[PM_PAR_SXX];
+        dPAR[PM_PAR_SYY]  = +4.0*q*py*py/PAR[PM_PAR_SYY];
         dPAR[PM_PAR_SXY]  = -q*X*Y;
         dPAR[PM_PAR_7]    = -t*z;