n A test employing a diamond indenter whose point is an obtuse pyramid that makes an indentation of length seven times its width. This tester makes smaller, shallower indentations than Brinell or Vickers, suiting it to testing hardnesses of surfaces, as in case-hardened steel, or coatings. The Knoop hardness number (KHN) is equal to 14.2 P/L2, where P = the applied load in grams and L = the length in millimeters of the long axis of the indentation. (Handbook of physical polymer testing, vol 50. Brown R (ed). Marcel Dekker, New York, 1999; www.astm.org).