ISO 6507-2:2018 specifies a method of verification and calibration of testing machines and diagonal measuring system for determining Vickers hardness in accordance with ISO 6507‑1. A direct method of verification and calibration is specified for the testing machine, indenter and the diagonal length measuring system. An indirect verification method using reference blocks is specified for the overall checking of the machine. If a testing machine is also to be used for other methods of hardness testing, it shall be verified independently for each method. ISO 6507-2:2018 is also applicable to portable hardness testing machines but not applicable to hardness testing machines based on different measurement principles, e.g. ultrasonic impedance method.