A number derived from the net increase in depth of impression. Rockwell hardness numbers are always quoted with a scale symbol representing the penetrator, load and dial used. Rockwell hardness test results are used as indications of the formability of sheet material and to express tempers. When a Rockwell Hardness Test forces a cone–shaped diamond or carbide ball into the specimen being tested under standard pressure, the depth of penetration is an indication of the Rockwell Hardness.

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