In November 2018, the International Committee for Weights and Measures (Comité international des poids et mesures, CIPM) held its quadrennial General Conference on Weights and Measures (Conférence Générale des Poids et Mesures, CGPM). 

The CGPM is the conference where major decisions are made regarding, amongst other things, the Système International d'Unités, i.e. the “SI”.  It is normally held in Paris but this year was held in Versailles, literally a stone’s throw from the Palace of Versailles.

I was lucky enough to attend the CGPM as part of the delegation from the International Commission on Illumination (the Commission Internationale de l'Eclairage, CIE), the global peak scientific and standardising body in matters relating to light and lighting and a liaison organisation to the CIPM.

This particular CGPM was an historic occasion, in that the meeting officially approved a resolution to fundamentally revise the SI.  And so, from World Metrology day on 20th May 2019 the SI will be based on seven physical constants, and thus inherently stable.  This will also mark the end of the last remaining physical artefact in the SI system – a cylinder of metal known as the International Prototype of the Kilogram.

The CGPM itself ran for four days and was an amazing event to be involved in.  There were interesting talks on many aspects of metrology and the opportunity to meet people from all over the globe.  I was particularly impressed by the number of attendees from Africa – I had no idea that there was such an advanced cooperation in metrology in the region.  On the morning of the momentous vote to redefine the SI, dozens of high school and university students were in attendance: a great promotion of metrology to the next generation of metrologists!

The Australian delegation was headed by Dr Bruce Warrington, Chief Metrologist of Australia’s National Measurement Institute, and New Zealand was represented by Dr Fleur Francois, Director of the Measurement Standards Laboratory of New Zealand.

For more information on the redefinition of the SI and to view some of the talks from the CGPM, see and and

Tony Bergen
Technical Director
Photometric Solutions International

Below: The CIE Delegation to the CGPM (left to right) Tony Bergen, CIE Division 2 Secretary and CIE Division 2 Director-elect; Kathryn Nield, CIE General Secretary; Yoshi Ohno, CIE President; Peter Blattner, CIE Division 2 Director and CIE President-elect

Below: During the CGPM Presentation on the redefinition of the Kilogram by Phillipe Richard, Director of METAS.