In this video we see the process for inspection and reconditioning granite surface plates. The plates are inspected and calibrated with an Autocollimator and a special instrument called a repeat meter sensitive to millionths of an inch. The plates can be resurfaced in the field using diamond charged cast iron laps. For more information or to get your plates calibrated check out the links below.
http://www.standridgegranite.com/
http://www.precisiongraniteusa.com/