Editing Caesium (section)

====Definition of the second====
The second, symbol ''s'', is the SI unit of time. The [[BIPM]] restated its definition at its 26th conference in 2018: "[The second] is defined by taking the fixed numerical value of the caesium frequency {{math|Δ''ν''<sub>Cs</sub>}}, the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be {{val|9192631770}} when expressed in the unit [[Hz]], which is equal to s<sup>−1</sup>."<ref>{{cite web |title=Resolution 1 of the 26th CGPM |url=https://www.bipm.org/en/CGPM/db/26/1/ |publisher=Bureau International des Poids et Mesures |location=Paris |pages=472 of the official French publication |language=FR,EN |date=2018 |access-date=2019-12-29 |archive-date=2021-02-04 |archive-url=https://web.archive.org/web/20210204120336/https://www.bipm.org/en/CGPM/db/26/1/ |url-status=dead }}</ref>