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Caesium standard
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=== Amount of substance === The mole is [[Avogadro constant|an extremely large number]] of "elementary entities" (i.e. [[atoms]], [[molecules]], [[ions]], etc). From 1969 to 2019, this number was 0.012 Γ the mass ratio between the IPK and a [[Isotopes of carbon|carbon 12 atom]].<ref>{{Cite web|url=https://www.bipm.org/en/history-si/mole|title=Mole - BIPM}}</ref> The 2019 revision simplified this by assigning the Avogadro constant the exact value {{val|6.02214076|e=23}} elementary entities per mole, thus, uniquely among the base units, the mole maintained its independence from the caesium standard: * 1 [[Mole (unit)|mole]], mol, = {{val|6.02214076|e=23}} elementary entities * 1 [[katal]], kat, = 1 mol/s = {{sfrac|{{val|6.02214076|e=14}}|{{val|9.19263177}}}} elementary entities/{{math|Ξ''t''<sub>Cs</sub>}}
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