Knoop hardness test

The Knoop hardness test is a microhardness test - a test for mechanical diamond point is pressed into the polished surface of the test material with a known force, for a specified dwell time, and the resulting indentation is measured using a microscope. The Knoop hardness HK or KHN is then given by the formula:

$HK={{load(\mbox{kgf})} \over {impression area (\mbox{mm}^2)}}={P \over {C_pL^2}}$