1. A method for calculating a process center for a chuck in a processing chamber, comprising: generating a set of pre-processing measurement data points including measuring thickness of a substrate having thereon a film before substrate processing, said measuring occurring at a set of orientations and at a set of distances from a geometric center of said substrate; generating a set of post-processing measurement data points including measuring thickness of said substrate after said substrate processing, said measuring occurring at least at said set of orientations and said set of distances from said geometric center of said substrate; comparing said set of pre-processing measurement data points with said set of post- processing measurement data points to calculate a set of etch depth numbers; generating a set of etch profiles for said set of orientations; extrapolating a set of radiuses from said set of etch profiles, said set of radiuses being associated with a first etch depth; generating an off-centered plot, said off-centered plot being a graphical representation of said set of radiuses versus said set of orientations; and calculating said process center by applying a curve-fitting equation to said off-centered plot.