In a periodic verification, the accuracy of the hardness tester is checked by measuring the hardness of calibrated test blocks. This check is typically performed by the user himself. It is recommended that the hardness range of the test block be approximately the same as that for which the testing machine is used.
Periodic verification of the hardness tester by the user is mandatory under the following standards:
- Brinell: ISO 6506, ASTM E10;
- Rockwell: ISO 6508, ASTM E18;
- Knoop: ASTM E92;
- Vickers: ASTM E92.
The time intervals and scope of the periodic verifications are regulated differently, depending on the standard and the test method (see graph). Periodic verifications should also be documented.