Rockwell Hardness, or the Rockwell scale, is a hardness scale based on indentation hardness of the steel. The Rockwell test determines hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload.  When testing metals, indentation hardness correlates directly with tensile strength.  This important relation permits nondestructive testing of metals with portable equipment.  Higher Rockwell Hardness indicates stronger steel, but also indicates less flexible steel.