It is flat within µm (µm micron = mm) measured form a corner across the surface. Reference and Feeler Gages. First off, the top surface of the granite plate is the business surface, the sides and bottom of the plate are not certified. The bottom of the stone is generally parallel to the top, and pretty flat.
Granite surface plate calibration should be performed routinely to maintain the proper flatness and ensure measurement accuracy over time. The intervals between each surface plate calibration depends on the condition of the environment where the surface plate is located. This bugger is heavy, find a good place and leave it there it is not exactly portable. Dimensional Gauge is most respected in the Aerospace, Energy and Automotive sectors and is the most technically competent provider of granite plate repair and recertification that is available. Extend Plate Life Following a few guidelines will reduce wear on a granite surface plate and ultimately, extend its life.
First, it is important to keep the plate clean. How often should a surface plate be calibrated? A) This depends on the plate usage and environment.
We recommend that a new plate or precision granite accessory receive a full recalibration within one year of purchase. If the plate will see heavy use, it may be advisable to shorten this interval to six months.

