Check your hardness tester for accuracy against a block with a known hardness rating. Each block is tested according to ASTM E10, which checks the hardness at five locations along the block. They include a certificate that lists the block’s actual hardness, as well as each of the five measurements taken during the test. Blocks also include a NIST-traceable certificate that states they’ve passed a test for accuracy.

Each block is marked with their Brinell hardness rating and a serial number.