How exactly is traceability of measurement values achieved for instruments and equipment? There are 3 ways

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Laboratories can achieve traceability of measurement values through the following 3 methods (in other words: ensuring that measurement results can be traced back to the International System of Units (SI)): 1. Calibration provided by qualified laboratories. Calibration provided by qualified laboratories, for example, calibration certificates issued by CNAS-accredited calibration laboratories； Calibration certificate provided by a calibration laboratory accredited by A2LA in the United States ； Calibration certificates issued by calibration laboratories under the ILAC agreement are all recognized. 2. Standard values of certified reference materials traceable to the SI. Standard values of certified reference materials that are traceable to the SI ； The reference materials mentioned here refer to certified reference materials that can be traced back to SI units. It’s CRM, not RM. For example: GBW 08675, a standard material in the form of methylmercury solution, is a certified standard material whose values can be traced back to SI units. 3. Direct realization of SI units: The direct realization of SI units is ensured through direct or indirect comparison with ** or international standards. Here, it specifically refers to the National Institute of Metrology of China, which is the highest metrology institution in China. 4. Based on 1) Clause 7.6 of CNAS-RL01 and 2) Clause 6.5 of CNAS-CL01