This part of ISO 6506 specifies a method of verification and calibration of testing machines used for determining Brinell hardness in accordance with ISO 6506-1. It specifies a direct method for checking the main functions of machine operation and an indirect method suitable for the overall checking of the machine. The indirect method may be used independently for periodic routine checking of machine operation while in service. If a testing machine is also to be used for other methods of hardness testing, it should be verified independently for each method. This part of ISO 6506 is also applicable to portable hardness testing machines.