The calotester, also known as a ball craterer or coating thickness tester, is a simple equipment used to measure the thickness of coatings. It is also used to measure the amount of coating wear after a wear test carried out using a “pin-on-disc” tester. The calotester consists of a holder for the surface to be tested and a steel sphere of known diameter that is rotated against the surface by a rotating shaft connected to a motor whilst diamond paste is applied to the contact area. The sphere is rotated for a short period of time but due to the abrasive nature of the diamond paste this is sufficient time to wear a crater through thin coatings.