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Hardness testing has long been used as a simple, convenient method of checking the characteristics of metallic alloys as affected by composition, heat treatment, cold working or other fabrication operations. Hardness is defined as the resistance to plastic deformation under indentation loading, but it is also used to describe resistance to scratching or cutting. Its usefulness stems partly from the fact that hardness correlates fairly closely with the tensile strength of the material as measured in a standard tension test. See Fig. 1. Hardness is often measured as the load divided by the indentation area supporting the load, thus with the dimensions of kg/mm2.