During the DMM calibration process, the instrument is compared against a known reference source, typically a standard resistor or a voltage source, to ensure that it is measuring accurately. The calibration process involves a series of tests at different ranges and the results are compared with the reference values. Calibration certificates are then provided to document the calibration process and results, providing traceability and peace of mind for the customers.

Regular calibration of DMMs is essential to ensure accurate measurements, as the accuracy of the instrument can drift over time due to various factors such as aging, mechanical shock, and exposure to extreme conditions. The frequency of calibration depends on several factors, including the industry, application, and the frequency of use. Typically, DMMs should be calibrated at least once a year, but some applications may require more frequent calibration.