Proefkilogram

Proefkilogram is a Dutch term that translates roughly as "test kilogram." In metrology, it refers to a kilogram-scale mass artifact used as a working reference for the calibration and testing of weighing equipment. A proefkilogram serves to verify the accuracy, stability, and line­arity of scales, balances, and mass comparators, and to ensure traceability of mass measurements to the kilogram.

Historically, national metrology institutes maintained such test masses to support routine calibration activities and to provide a stable reference within the national measurement system. While the International Prototype Kilogram (IPK) acted as the international standard, a proefkilogram functioned as a practical, locally accessible artifact for everyday calibration and quality control. The concept emphasizes practical reliability and traceability rather than international primacy.

With the 2019 redefinition of the kilogram, which bases the unit on the Planck constant rather than a physical artifact, the role of working masses shifts away from defining the unit itself. Nevertheless, physical kilogram masses continue to be used as calibration references in laboratories and in legal metrology for device verification, both to disseminate the unit and to support measurement confidence in routine applications.

See also: International Prototype Kilogram, Planck constant, metrology, calibration weight, legal metrology.