SI base unit units are written in lowercase, except the symbols of those named after a person, which are written with an initial capital letter. For example, the "metre" (US English: "meter") has the symbol m, but the "kelvin" has symbol K, because it is named after Lord Kelvin and the "ampere" with symbol A is named after André-Marie Ampère. Several other units, such as the litre (US English: "liter"), are formally not part of the SI, but are accepted for use with SI. New definitions of the base units were approved on 16 November 2018, to take effect 20 May 2019. The
Atomic mass unit names for the same unit of measure. As with other unit names such as watt and newton, "dalton" is not capitalized in English, but its symbol, Da, is capitalized. With the introduction of the name "dalton", there has been a gradual change towards using that name in preference to the name, "unified atomic mass unit": The former definition of the mole, an SI base unit, was accepted by the CGPM in 1971 as: However, the first part of this definition was changed in 2018 to: One consequence of this change is that the current defined relationship between the mass of