GB/T 21838.2-2008 The inspection and calibrating of testing machines in the determination of hardness of materials and parameters of focused metals. The accuracy of instrumented indentation tests depends on the state of the testing machine. The standard is clearly applicable to various types of testing machines for such tests. The inspection and calibrating process of the testing machine is specified in detail, covering the calibration method of key parameters such as force value and displacement, and the calibration period and allowable error range are clarified. The selection and use requirements of standard blocks for calibrating are also explained. Through standardized operation, the testing machine is ensured to be accurate and reliable, providing a stable and accurate basis for subsequent measurement of metal hardness of materials and related parameters, and ensuring the credibility of test results.