Each test block has been calibrated on a hardness tester whose accuracy has been verified using N.I.S.T. traceable load and depth measuring devices. The test blocks are made from only the highest quality material to ensure complete uniformity and repeatability. They are hand lapped and polished to a mirror finish. Each test block is calibrated and marked with its own unique serial number along with the serial number of the indenter or penetrator in the calibration set that they were produced with. Each block comes with the latest test block certification requirements from ASTM and NIST, providing you with the most comprehensive calibration test block available.