Project: Realisation of the awaited definition of the kilogram - resolving the discrepancies

The mass of the international prototype of the kilogram, which is 1 kg by definition, is drifting with respect to the mass of its official copies over time. In order to redefine the kilogram in terms of fundamental physical constants, there needs to be international agreement on the Planck constant and on the Avogadro constant. Two experiments have so far achieved accuracies close to the requirements: a watt-balance experiment linking mechanical and electrical power, at the National Institute of Standards and Technology (NIST) in the USA, and a silicon sphere experiment carried out by the International Avogadro Coordination (IAC). However, there is a discrepancy between the values measured in these two experiments, which indicates error in at least one of them. This project aims to understand what this error is and to remedy it by delivering a European watt-balance determination of the Planck constant while also refining measurements and repeating the Avogadro determination. This will lead to lower uncertainties and it is a step towards the redefinition of the SI unit of mass.

Acronym SIB03 kNOW (Reference Number: SIB03)
Duration 01/09/2012 - 31/08/2015
Project Topic Metrology
Project Results
(after finalisation)
See Website
Website visit project website
Network EMRP
Call EMRP Call 2011 - Health, SI Broader Scope and New Technologies

Project partner

Number Name Role Country
1 Istituto Nazionale di Ricerca Metrologica Coordinator Italy
2 Conservatoire national des arts et metiers Partner France
3 Eidgenössisches Institut für Metrologie METAS Partner Switzerland
4 Laboratoire national de métrologie et d'essais Partner France
5 Observatoire de Paris Partner France
6 Physikalisch-Technische Bundesanstalt Partner Germany
7 National Institute of Advanced Industrial Science and Technology Observer Japan
8 Leibniz-Institut für Oberflächenmodifizierung Observer Germany
9 Leibniz-Institut für Oberflächenmodifizierung Germany