Just for the record, most, if not all categorically, CMM tables are not certified as flat like surface plates. They develop their own base plane of reference from points measured by the probe, either a hard probe or a touch probe like a Reneshaw. They are generally very thick for their size, and do contain threaded metal inserts to hold inspection fixtures, etc. at times. They can, however, be lapped and certified to the same specifications as granite surface plates, but for the most part, inspection departments do not bother, since it isn't used as a surface plate.