This part of ISO 4545 specifies the method of verification and calibration of testing machines for determining Knoop hardness for metallic materials in accordance with ISO 4545-1. It covers test forces from 0,0098 07 N to 19,614 N. The method is recommended only for indentations with diagonals ðe" 0,020 mm. It specifies a direct method of verification and calibration of the testing machine and the diagonal length measuring system for determining Knoop hardness and an indirect verification method suitable for the overall checking of the machine. The indirect verification method may be used on its own for periodic routine checking of the machine in service. If a testing machine is also to be used for other methods of hardness testing, it shall be verified independently for each method.