The Rockwell scale is a hardness scale used to measure the hardness of materials. It is based on the indentation of a diamond cone or hardened steel ball into the surface of the material. The hardness value is then determined by measuring the depth of the indentation and comparing it to a reference chart. The Rockwell scale has several different scales, each designed to measure different types of materials. The most commonly used scales are the A, B, C, and E scales.