(a) Indentation made by square-base diamond-pyramid indenter used in Vickers hardness test.
D, mean diagonal of the indentation in millimeters. (b) Indentation made by rhombus-base
diamond-pyramid indenter used in Knoop hardness test, together with scale. (c) Comparison of
Knoop and Vickers indentations. Source: Metallurgy for the Nonmetallurgist, Harry Chandler, ASM
International, p 204, 1998.