A company operating with a Quality System certified according to ISO 9001 must verify all weighing instruments at their disposal on a periodic basis, the frequency of which is to be determined at the discretion of the company in combination with their Quality Inspector and depends on the use for which the instrument is intended.

If the weighing instrument is crucial to the major activities of the company and is used with high frequency, the required verification period may even be monthly or half-yearly, but if the weighing instrument is used rarely, e.g. for minor activities within the company, inspections should be less frequent, for example every 2-3 years.

The verification can be carried out using certified weights traceable to national standards, following a properly documented procedure.