Requirements of weighing in legal metrology

A review is given of recent developments in the formulation of requirements of weighing where such measurements are performed in society and industry with legal implications such as safety, fair trade and environmental considerations. Traditional legal metrology in the area of weights and measures has been developed and given an expanded scope in recent years. This reflects, on the one hand, technical and scientific development (computerization of weighing devices, improved weight manufacturing and new methods of magnetism determination, for example), and on the other hand, administrative evolution (global requirements of the market and the Measurement Instrument Directive). Particularly fruitful has been the joint effort by the scientific mass metrology and legal metrology communities in the development in the last decade of international recommendations—especially OIML R111—on weighing. Consensus has been reached in the international weighing forum concerning important areas such as maximum permissible errors for weights, how to calculate measurement uncertainty and how measurement uncertainty should be accounted for in relation to conformity assessment. These international recommendations for weights as mass standards include both tolerances and extensive instructions about various influence quantities that affect the weight result, such as magnetization, surface roughness and volume of weights. Much remains to be done, however: corresponding requirements of weighing devices in particular need to meet the challenges of a rapidly changing technology. The promising collaboration between scientific and legal metrology initiated in the area of weights may act as a model and stimulate similar developments in other areas of metrology, particularly where requirements are generic (for instance uncertainty and conformity) or analogous.