Legal metrology rules apply to commercial transactions in which a product is sold by weight, or weight is the basis for a tariff etc. To undertake such transactions, weighing equipment must be approved for this use, verified by the relevant local weights and measures authorities, and marked to identify it as being subject to legal metrology.
Recommendation R 76-1 from the International Organization of Legal Metrology (OIML) and Handbook 44 from the National Institute of Standards and Technology (NIST) provide guidance on the correct selection and use of weighing equipment and include detailed information on approval, verification, and marking. However, the guidance in these publications does not, and cannot, cover the vast array of commercial applications that exist. Even if the guidance is followed precisely, it is possible that individual quality requirements may not be fulfilled. In particular, the guidance is insufficient for weighing very small quantities.
Furthermore, yearly or bi-yearly verification of weighing equipment according to local or national rules may not be sufficient to detect a drift or any deterioration in its performance. An assessment of the risk of the consequences of an incorrect weighing result should form the basis for the frequency of performance verification.
In this white paper, the limitations of legal metrology rules are highlighted. Science-based solutions are presented that ensure accuracy and quality requirements as well as the requirements for regulated markets are fulfilled. These include understanding the minimum weight of the balance or scale and applying a risk-based approach to routine testing. The procedures described will help you to select the right weighing equipment for your needs as well as assess if your current weighing instruments are fit for purpose
