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On the possible future revision of the SI
Towards the "New SI"...

At its 24th meeting (October 2011) the CGPM adopted a Resolution on the possible future revision of the International System of Units (the SI). This Resolution takes note of the CIPM's intention to propose a revision of the SI, and sets out a detailed road-map towards the future changes.

Resolution 1 of the CGPM (2011): On the possible future revision of the International System of Units, the SI

In the "New SI" four of the SI base units, namely the kilogram, the ampere, the kelvin and the mole, will be redefined in terms of invariants of nature; the new definitions will be based on fixed numerical values of the Planck constant (h), the elementary charge (e), the Boltzmann constant (k), and the Avogadro constant (NA), respectively. Further, the definitions of all seven base units of the SI will also be uniformly expressed using the explicit-constant formulation, and specific mises en pratique will be drawn up to explain the realization of the definitions of each of the base units in a practical way.

While remarkable progress has been made over the last few years, the conditions for adopting the redefinitions, as set by the CGPM at its 23rd meeting (2007), have not yet been fully met. The CGPM encourages National Metrology Institutes, the BIPM and academic institutions to maintain their efforts towards the experimental determination of the fundamental constants h, e, k and NA.

In order to encourage communication, awareness and debate on the possible revision of the SI, access is given here to the following key document, which is currently at draft stage and will be amended in the coming years:

(Draft dated 16 December 2013)
Why change the SI?
What changes are proposed?
The "explicit-constant" formulation
What is a mise en pratique?
When might the changes take place?
What is the BIPM contributing?
Discussions on the New SI in the Consultative Committees
Discussion in the scientific literature
FAQs, Frequently Asked Questions about the New SI