A method for testing the hardness of metals by
determining the depth of penetration of a steel
ball or a diamond sphero-conical indentor. The
value is read from a dial and is an arbitrary
number related to the depth of penetration. 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.