Abstract
Each coherent system of units is based on a system of quantities in such a way that the equations between the numerical values expressed in coherent units have exactly the same form, including numerical factors, as the corresponding equations between the quantities. The highest international body responsible for the International System of Units (SI) is the Conférence Générale des Poids et Mesures (CGPM). However, the CGPM is not concerned with quantities or systems of quantities. That question lies within the scope of Technical Committee number twelve of the International Organization for Standardization (ISO/TC 12). Quantities, units, symbols, conversion factors. To fulfil its responsibility, ISO/TC 12 has prepared the International Standard ISO 31, Quantities and Units, which consists of fourteen parts. The new editions of the different parts of the International Standard are briefly presented here.