Use two lists of PAS images to determine mean images centroids (via the header OBICX,OBICY values) and then the mean image offsets.
% pas_XY_offsets.sh --helpThe resultant output is a list of statistics for the mean linear offset (i.e. the value of R = sqrt{dX^2 + dY^2}).
Note that PAS image lists are presumed to be a set of images for the same field. The second list of images is presumed to be of the same field (with the same bright source measured) after a small telescope offset has been performed. You can do the same sort of calculation shown here using ds9_imstats centroids with table_XY_offsets.sh.