The SI — the modern metric system — has seven base units from which all other measurement units can be derived. On May 20, 2019, four of them — the kilogram, kelvin, ampere and mole — were redefined in terms of constants of nature. The remaining three — the second, meter, and candela — are already based on universal constants.

As of March 2013 the proposed redefinition is known as the "New SI" [3] but Mohr, in a paper following the CGPM proposal but predating the formal CCU proposal, suggested that because the proposed system makes use of atomic scale phenomena rather than macroscopic phenomena, it should be called the "Quantum SI System".

The International System of Units, the SI (Système International d’unités), provides the internationally agreed means by which we make such measurements. At a meeting of the General Conference on Weights and Measures (CGPM) held in Paris on 16 November 2018 a new and revised SI was approved, adapted for the 21st century.*

2022年11月17日 · New prefixes in the International System of Units have been confirmed, ushering in ronto and quecto for tiny numbers and ronna and quetta for very large numbers, like the amount of data on ...

2023年1月4日 · In December 2022, the BIPM SI Brochure (9 th Edition, December 2022, V2.01) was published to include the four new International System of Units (SI) prefixes recently adopted by the General Conference on Weights and Measures (CGPM) in November 2022. The SI prefixes were expanded from 20 to 24 with the addition of ronna, ronto, quetta, and ...

2016年1月7日 · Following the introduction of the ampere, the kelvin and the candela as the units for electric current, thermodynamic temperature and luminous intensity, respectively, the name Système ...

2021年12月6日 · Lessons and activities focus on physical science and mathematics related to the new International System of Units (SI). Explore themes that include redefining measurement, pursuing accuracy, achieving precision, and measurement process innovation.

2020年10月16日 · In the new SI, the units of mass (kg), electric current (A), temperature (K) and quantity of substance (mol) are redefined by linking them to the four universal constants that appear in table 1, whereas the units of time (s), length (m) and luminous efficacy (cd) remain associated with constants of nature as before (see figure 2).

2011年12月11日 · The decision to replace m( 𝒦), μ 0, T TPW, and M(12 C) in the current SI with h, e, k, and N A to establish the New SI is based in part on experimental advances made over the last several decades in using the Josephson effect (JE) to measure voltage, the quantum hall effect (QHE) to measure resistance, and acoustic gas thermometry (AGT) to ...

The new SI is a universal and highly stable unit system based on invariable constants of nature. Its implementation rests on quantum metrology and quantum standards, which base measurements on the manipulation and counting of single quantum objects, such as electrons, photons, ions, and flux quanta.