Accurately measuring mass is fundamental to many areas of everyday life. From sophisticated manufacturing processes to microgram drug delivery or environmental monitoring - all rely on accurate weight measurements traceable to the SI kilogram. Currently the kilogram is determined by a physical artefact maintained in air at the BIPM in Paris. Copies are held around the world and periodic comparisons with the original have revealed small but significant weight changes over time. To resolve this issue, a redefinition in terms of a fundamental physical constant - the Planck constant - is proposed.

Experimentally determining the kilogram, after its proposed redefinition, will either be based on Kibble balance experiments that compare electrical and mechanical power, or by the X-ray crystal density (Avogadro) experiment that counts atoms in a silicon sphere using x-rays and optical interferometry. Both approaches are complex, requiring a wide range of measurement skills and specialist equipment.

EMRP projects Realisation of the awaited definition of the kilogram - resolving the discrepancies and Developing a practical means of disseminating the new kilogram helped to resolve the small remaining differences between the Kibble balance and Avogadro practical realisations of the kilogram. This ensures there will be no discontinuity between current and future mass measurements after the kilograms redefinition.