Analysis of definitions of key metrological terms in the International System of Units

In preparation for the reform of the International System of Units at the 26th General Conference on Weights and Measures in 2018, the Consultative Committee for Units of the International Committee for Weights and Measures proposed, along with changing the definitions of the four base units (kilogram, ampere, kelvin and mole), also changing the definition of the term unit of quantity. This proposal caused a wide discussion in the metrology community and was not accepted by the majority of participants in the discussion. It was decided to continue the discussion of this issue after the 26th General Conference on Weights and Measures. The article analyzes the definitions of the key metrological terms quantity, unit of quantity, value of quantity presented in the SI Brochure, the standards of the International Organization for Standardization, the International Vocabulary of Metrology and the proposals of the working group on key metrological terms created by the Consultative Committee for Units in 2019. It is shown that in all of the listed publications, the definitions of these terms have both physical, mathematical and linguistic inaccuracies and inconsistencies.