ASTM E10. A common standard method of measuring the hardness of metallic materials. A hardened steel or tungsten carbide ball is pressed into the smooth surface of the material with a specific load. A microscope in used to measure the diameter of the indentation in the material surface and then compared to the corresponding Brinell Hardness Number (BHN) on a chart or calculated from a prescribed formula, the applied load in kilograms divided by the surface area of the resulting impression in square millimeters. The Brinell hardness test for steel involves impressing a 10 mm diameter hardened steel or tungsten carbide ball with a load of 3000 kilograms. The Vickers hardness scale is preferred for steels with a hardness over 500 BHN.