On May 20th, the world metrology day, the Bureau International des Poids et Mesures (BIPM) announced a major revision of four of the seven basic units of the International System of Units (SI). The method of Single-Pressure Refractive Index Gas Thermometry which was jointly developed by Technical Institute of Physics and Chemistry, Chinese Academy of Sciences (TIPC-CAS) and Laboratoire national de métrologie et d'essais-Conservatoire national des arts et métiers (LNE-Cnam) was included in the implementation plan of kelvin -- Mise en pratique for the definition of the kelvin in the SI (MeP-K). Researchers from TIPC-CAS and scientists from other six countries, including the United Kingdom, the United States, France, Canada, Germany, and Italy, have jointly written the relevant technical documents. 

In November 2018, the No.1 resolution: ‘Revision of the International Scale of Units’ was unanimously adopted on the 26th International Metrology Conference (CGPM) in which four SI basic units, Kilogram, Ampere, Kelvin and Mole, will be defined by the Planck constant, the elementary charge, the Boltzmann constant and the Avogadro constant. The new definition will be officially effective on May 20th, 2019. In the research of redefining the kelvin by fixing the Boltzmann constant, the team from LNE-Cnam (TIPC-CAS participated) reached relative uncertainty of 0.6ppm (1ppm=10-6), which was the best result among the data adopted by the Committee on Data for Science and Technology (CODATA) for this constant.

For the related link, you can press:　　https://www.bipm.org/en/publications/mises-en-pratique/ 

The work was financially supported by the National Key R&D Program of China, the National Natural Science Foundation of China, and the the International Partnership Program of the Chinese Academy of Sciences.