Indentation hardness test, performed with either 3 gf or 9 gf loads, preceded the development of microhardness testers using traditional indenters. In 1925, Smith and Sandland of the UK developed an indentation test that employed a square-based pyramidal indenter made from diamond. They chose the pyramidal shape with an angle of 136° between opposite faces in order to obtain hardness numbers that would be as close as possible to Brinell hardness numbers for the specimen. The Vickers test has a great advantage of using one hardness scale to test all materials.The first reference to the Vickers indenter with low loads was made
Ringelmann scale are equivalent to an opacity of 0, 20, 40, 60, 80 and 100. Some agencies issue cards that can be compared to the smoke while others use apps on phones. Ringelmann scale The Ringelmann scale is a scale for measuring the apparent density or opacity of Smoke. It was developed by a French professor of agricultural engineering Maximilien Ringelmann of La Station d'Essais de Machines in Paris in 1888. Ringelmann also discovered what is now called the Ringelmann effect. The scale is has a 5 levels of density inferred from a grid of black lines on a white surface which,