A measure of hardness (resistance to indentation) obtained by applying a load--through use of a ball indenter--and measuring the permanent impression in the material. The hardness value of aluminium alloys is obtained by applying a load of 500 kilogrammes to a ball 10 millimetres in diameter for 30 seconds; the applied load (in kilograms) is divided by the spherical area of the impression (in square millimeters).