The Rockwell scale is a hardness scale used to measure the hardness of metals, plastics, and other materials. The scale is based on the indentation hardness of a material, which is determined by measuring the depth of an indentation made by pressing a diamond cone or hardened steel ball into the surface of the material. The Rockwell scale is divided into three different scales: A, B, and C. Each scale has its own range of values that indicate increasing levels of hardness.