Hardness testers are devices that indicates the hardness of a material, usually by measuring the effect on its surface of a localized penetration by a standardized rounded or pointed indenter of diamond, carbide, or hard steel.

Hardness testing is a widely used method for measuring hardness. This test is based on the principle that the amplitude of oscillation of a rocking device decreases the softness of the surface of a coating on which the test is performed more rapidly. The tester automatically records the number of swings made by a standard rocker in contact with the test sample and is rolled to the right until the bubble in the left-hand vial is visible. The rocker is then released and each total appearance of the bubble in the right-hand vial is counted. The counter is stopped when the bubble is no longer seen.