Primary method for realizing the kilogram
Primary mass standard (artefacts calibrated by primary methods)
The definition of the unit of mass does not imply or suggest any particular method to realize it. Currently, there are two primary methods of practical realization of the mass unit based on its formal definition. A primary method is a method for determining a mass in terms of h without use of any other mass standard. The mass whose value is to be determined may be an artefact, atom or other entity although the focuses on metrology for mass artefacts at the highest level of accuracy. Such an artefact whose mass has been directly calibrated by a primary method to realize the kilogram definition is called the primary mass standard. Secondary mass standards are established through calibration with respect to primary mass standards.
At the SCL, the silicon sphere is one of the primary mass standards and the unit of mass, the kilogram, is disseminated from these mass standards.
Reference
- Mise en pratique for the definition of the kilogram, prepared by the Consultative Committee for Mass and Related Quantities (CCM).