There are three types of tests used to ensure accuracy. The Brinell hardness test, Rockwell hardness test and the Vickers hardness test.
The definitions of metallurgic ultimate strength and hardness are rather similar. It can generally be assumed that a strong metal is also a hard metal. The way in which the three of these hardness tests measure a metals hardness is determined upon the metals resistance to the penetration of a non-deformable ball or cone.
The tests determine the depth at which such a ball or cone will sink into the metal, under a given load, within a specific period of time.