1.1 This specification covers weights and mass standards used in laboratories, specifically classes 0, 1, 2, 3, 4, 5, 6 and 7. This specification replaces National Bureau of Standards Circular 547, Section 1, which is out of print.

1.2 This specification further recognizes that International Recommendation R111 exists, that describes classes E1, E2, F1, F2, M1, M2 and M3. Users may choose to reference either R111 or this specification, depending on requirements.

1.3 This specification contains the principal physical characteristics and metrological requirements for weights that are used.

1.3.1 For the verification of weighing instruments;

1.3.2 For the verification of weights of a lower class of accuracy; and

1.3.3 With weighing instruments.

1.4 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.

1.5 The values stated in SI units are to be regarded as the standard.