First, determine the verification and calibration requirements of measuring instruments. The verification method of non-mandatory verification measuring instruments can be determined by the enterprise according to the needs of production and scientific research. It can be calibrated in the unit or sent to other metrological verification institutions for verification, testing and calibration. The highest metrological standard instruments used by the enterprise, as well as the working metrological instruments included in the mandatory verification catalog for trade settlement, safety protection, medical and health, and environmental monitoring, shall be subject to mandatory verification. 2. Select a third-party verification agency that meets the requirements. Send the calibration requirements of the instrument manufacturer to the third-party calibration agency and let the third-party calibration agency confirm whether it has the calibration capability. Whether the calibration certificate is recognized by the auditor depends on whether the defined calibration requirements meet the definition of the test standard/method and whether the results of the calibration parameters meet the specifications defined in the test standard/method. If all are met, the on-site auditor will not have any doubts about its traceability activities, and at most will confirm the evaluation activities of the selected calibration agency (supplier's evaluation activities). Since the calibration agency also belongs to the laboratory and is also subject to the CNAS accreditation rules, the calibration agency will not take the risk of issuing a calibration report that does not comply with the accreditation rules. 3. When determining whether the scope of the calibration supplier meets the laboratory's requirements, the general practice is to compare the name of your own equipment and measurement parameters with the CNAS scope of the calibration supplier. If the calibrated equipment is not within the scope of the calibration laboratory, it is usually measured according to the attributes of the equipment.