(1) Plot Collinearity Y(EVD+WVU) wrt position of EVD A-Plane-1st-strip-position or WVU A-Plane-1st-strip-position

(2) Calculate Collinearity with the cut ( yWVU>0.019 && yEVD<-0.018 )

 Before the cut ( Y(EVD+WVU) is at the bottom/right-handed corner):

 http://drupal.star.bnl.gov/STAR/system/files/deltax_deltay_vertical_10182006n.gif

After the cut,

Without the Gaussian fit, the mean values would change even larger (both 10182006) :

Before the cut:

After the cut:

By comparison, the Gaussian fit has tried its best to get it to be centered but still not enough.