This Recommendation includes metrological and technical requirements and test methods for the metrological control of digital, self-indicating measuring instruments used to determine the protein content of grain and oilseeds for commercial transactions. It specifies accuracy requirements including maximum permissible errors (MPEs) for verification and other error limits for type evaluation tests. The provisions in this Recommendation are based on the performance of instruments that estimate the mass fraction of protein constituents in grain and oilseeds via inferential means. Instruments that modify the test sample in order to infer the protein content are not specifically covered, but may still qualify for type approval if the requirements in the Recommendation are met. This Recommendation is not intended to preclude the application of new technologies to grain protein measurement.