When choosing a calibration service, the first thing to do is to check whether they have the corresponding calibration qualifications, which is also the premise for providing services. To verify that the calibration agency has the ability to measure the calibration parameters, it is necessary to verify the table attached to the certificate, including whether the measurement parameters have been approved by metrology or CNAS; whether the uncertainty or accuracy of the parameters meets the requirements for verification and calibration equipment. In addition, service quality and efficiency are key characteristics of the calibration service agency, including personnel, experience, equipment and its reputation in the market, which must be fully considered.