7. Calibration frequency

The mass of a weight varies little over time. The reasons for its wear are essentially due to its use and storage.

The evolution of a weight's value is proportional to its use. This evolution is calculated by the deviation of the weight value from one calibration certificate to the next, compared with the value of the measurement uncertainty.

It is important to determine a short calibration period (e.g. 12 months) and then, depending on the deviation calculation, to increase or shorten it. A common practice is to keep reference standards for five years, without recalibration, and working standards for one year. In all cases, it is preferable to use measurement results as a basis, rather than adopting a usage that is not recognized by the various certification bodies.