This Precision Granite Surface Plate is manufactured to meet or exceed the tolerances specified by Federal Specification GGG-P-463c. A Calibration Certificate is included with every surface plate guaranteeing overall surface flatness and repeat gage measurements, and is traceable to N.I.S.T. or equivalent National or International Organization, complies with, ANSI/NCSL Z540-1and ISO 10012 in accordance with our ISO 9001 certified quality system. Long-form certification is available. We are an accredited provider of 17025 Calibration Services.This Precision Granite Surface Plate is made of black granite which is stronger and denser than light colored granite, and more stable. The granite properties determine the stiffness of the granite so accuracies can be guaranteed with less thickness than other types of granite. This translates to less freight and handling whenever the plate is shipped or moved.