GB/T 43432.3-2023 "Metallic materials—Barcol hardness test—Part 3: Calibration of reference hardness blocks" specifies the calibration methods and technical requirements for reference hardness blocks used in the verification of Barcol hardness testers. It defines the material selection, microstructure, surface quality, and dimensional accuracy requirements for the reference blocks. Calibration must be conducted in an environment with a temperature range of 10°C to 35°C, and the number and spacing of indentations are standardized. Traceability of the hardness values is ensured through the use of standard equipment, guaranteeing the accuracy and uniformity of the hardness block values. This provides a reliable benchmark for the verification and calibration of Barcol hardness testers.