This part of ISO 7971 specifies a test method for ensuring the traceability of mass per hectolitre measuring instruments through reference to standard measurement instruments. The mass per hectolitre or bulk density is of commercial importance for grain cereals. Several types of instruments with varying performances exist for measuring it.This part of ISO 7971 also specifies the performances required of national standards instruments, secondary standards instruments, and measuring instruments used in laboratories or in collection or storage silos.