Stanley Rockwell invented the Rockwell hardness test to provide a fast, non-destructive method for determining the success of heat treatments on ball bearings. There are two types of Rockwell tests that use different combinations of indenters and loads to test a range of materials. The test involves applying and measuring the depth of two loads to determine the Rockwell hardness number, with higher numbers indicating harder materials. Common scales use diamond cone or steel ball indenters under various loads designated by letters like B, C, and D. The test takes only seconds to perform and can be used for quality control due to its speed and small, non-destructive indentation.