Rockwell hardness number (HR)

Number derived from the net increase in the depth of impression as the load on the indenter is increased from a fixed minor load to a major load and then returned to the minor load. The Rockwell hardness number is always quoted with a scale symbol representing the indenter, load and dial used. Rockwell A scale is used in connection with carbide cutting tools. Rockwell B and C scales are used in connection with workpiece materials.