What are OIML and ASTM Calibration Weight Classes?

OIML Weight Classes

Weight classes are separated according to the error limits that are classified either according to OIML (International Organization of Legal Metrology) or ASTM (American Society for Testing and Materials) declarations as follows.

Class E1 weights are intended to ensure traceability between national mass standards and weights of class E2 and lower (i.e. F1 and F2). Class E1 weights or weight sets shall be accompanied by a calibration certificate.

Class E2 weights are intended for use in the initial verification of class F1 weights and for use with weighing instruments of accuracy class I. Class E2 weights or weight sets shall always be accompanied by a calibration certificate.

Class F1 weights are intended for use in the initial verification of class F2 weights and for use with weighing instruments of accuracy class I and class II.

Class F2 weights are intended for use in the initial verification of class M1 and possibly class M2 weights. They are also intended for use in important commercial transactions (e.g. precious metals and stones) on weighing instruments of accuracy class II.

Class M1 weights are intended for use in the initial verification of class M2 weights and for use with weighing instruments of accuracy class III.

Class M2 weights are intended for use in the initial verification of class M3 weights and for use in general commercial transactions and with weighing instruments of accuracy class III.

Class M3 weights are intended for use with weighing instruments of accuracy class IIII.