Vickers Hardness of Materials
The Vickers hardness test method was developed in 1924 by Smith and Sandland, engineers at Vickers Ltd. in the UK. A square pyramid made of diamond is pressed into materials to be tested. The hardness, named the Vickers Pyramid Number, is calculated as the ratio of the applied force and the surface area of the indentation. The angle between two opposing faces of the pyramid is selected as 136° for the standard test.
For additional information see the relevant Wikipedia entry.