for measuring hardness
(resistance to penetration) of materials, expressed as a number assigned to the depth of penetration of a diamond cone or steel
ball. There are several scales of Rockwell hardness of which the A (for extremely hard materials), B (for medium hardness materials), and C (for the material
reading over 100 on the B-scale) are the most common
. Hardened tool
steel, for example, typically reads 62 on the C scale
, and is identified as 62Rc.