The General Conference on Weights and Measures (CGPM, for its acronym in French), which oversees the International System of Units (SI) system, will redefine four basic scientific units in November 2018: ampere, kilogram, kelvin and mol . The changes will take effect in May 2019. This is the largest revision of the IS since the establishment of this international reference system in 1960. The redefinitions of these units will be based on relationships with fundamental constants, rather than abstract constants or arbitrary definitions, as is the case today. This will allow scientists who work with the highest level of precision to do it in multiple ways, at any place or time and on any scale. In addition, these changes will not affect conventional scales.