The Rockwell scale is a hardness scale used to measure the hardness of materials. It is based on the indentation of a diamond-tipped cone or ball into the material being tested. The hardness number is determined by measuring the depth of the indentation and comparing it to a chart. The Rockwell scale is used in many industries, such as automotive, aerospace, and metalworking. It is also used to measure the hardness of metals, plastics, ceramics, and other materials.