GB/T 18449.3-2012 stipulates the calibration method of the standard Hardness block in the Knoop Hardness test of metal materials. The standard clarifies the calibration environmental conditions, describes the operation process in detail, and requires strict accuracy of the equipment used for calibration. The standard Hardness block is measured through the specification steps to accurately determine its Knoop Hardness value, ensuring that the Hardness value is accurate and traceable. The accurately calibrated Hardness block becomes the benchmark for calibrating Knoop hardness gauge, ensuring that the Knoop hardness testing results of metal materials are stable and reliable, and strongly supports the mass testing and performance evaluation of products in the metal industry.