Measure of resistance to penetration when material is exposed to a pointed load. The Rockwell Hardness measurement produces hardness numbers related to the depth of residual penetration of a steel ball or diamond cone (brale) after a minor load of 10 kilograms has been applied to hold the penetrator in position. Under this condition, the major load is applied (either 60, 100 or 150 kilograms). This residual penetration is automatically registered on a dial when the major load is removed from the penetrator but the minor load is still applied. Various dial readings combined with different major loads, five scales designated by letters varying from A to H; the B and C scales are most commonly in use. For testing hard steels, a sphero-conical diamond is used with a 150 kg load, the result is read from the black scale on the dial and is prefixed with the letter C. A hardened tool steel would typically give a reading of 62Rc. For softer metals Scale B is used with a 1/16" diameter steel ball and a standard load of 100 kgs.