1.1 This specification covers various classes of weights and mass standards used in laboratories. Weights used for commercial measurements are excluded, except that one class of standards designed for the calibration of commercial test weights is included. Tolerances and design restrictions for each class are described in order that both individual weights or sets of weights can be chosen for appropriate applications (see Note). In general, this specification replaces, in function, National Bureau of Standards Circular 547, Section 1, which is out of print.

Note-Although metric weights are almost exclusively used in laboratories, tolerances are given in this specification for nonmetric weights in U.S. customary units for all classes. It is anticipated that as metrication, even in test laboratories, proceeds further, the nonmetric tables given in this specification will become obsolete.

1.2 This specification recognizes International Recommendation No. 1 (cylindrical weights from 1 g to 10 kg of average precision) and International Recommendation No. 20 (weights of classes of precision E1, E2, F1, F2, and M1 from 50 kg to 1 mg). Where appropriate, it is recommended that these International Recommendations be used.