An apparatus for processing a substrate, the apparatus comprising a polishing assembly and a controller. The polishing assembly is configured to (a) polish a surface of the substrate. The controller is configured to (b) detect a first substrate measurement corresponding to a first region of the substrate, (c) detect a second substrate measurement corresponding to a second region of the substrate; (d) determine a difference between the first substrate measurement at the first region and the second substrate measurement at the second region; stop the polishing of the surface of the substrate in response to a determination that the difference between the first substrate measurement and the second substrate measurement is within a tolerance threshold; and repeat (a)-(d) in response to a determination that the difference between the first substrate measurement and the second substrate measurement is outside of the tolerance threshold.