Manufacturers worldwide have recoginized Standard E-100, defined by the American Society for Testing and Materials (ASTM) as the accepted parameters for hardness testing using the Rockwell method.

A rounded penetrator of known hardness is forced into the test surface under a specific pressure load. A crude hardness reading could be taken from the depth of penetration. Some inexpensive testers use this method.

To eliminate errors caused by surface variations, a minor load is applied and held while the tester is "zeroed". The real hardness reading measures the difference in penetration between the minor load and the major load.

Tester accuracy is checked by running the test on specimens of certified hardness.