The Rockwell hardness test method involves of  indenting the test material with a diamond cone or hardened steel ball indenter.  (Fig. 4A).

The indenter is forced into the test material under a preliminary minor load.

When equilibrium has been reached, an indicating device, which follows the movements of the indenter and so responds to changes in depth of penetration of the indenter, is set to a datum position.

 While the preliminary minor load is still applied an additional major load is applied with resulting increase in penetration

When equilibrium has again been reach, the additional major load is removed but the preliminary minor load is still maintained. Removal of the additional major load allows a partial recovery, so reducing the depth of penetration (Fig. 4C). The permanent increase in depth of penetration, resulting from the application and removal of the additional major load is used to calculate the Rockwell hardness number.