Named after the Belfast-born, Glasgow University engineer and physicist William Thomson (better known as Lord Kelvin), who first developed the concept of an absolute temperature scale, the kelvin is one of the seven base units in the International System of Units (systemé international, SI), along with the kilogram, ampere, metre, second, mole and candela.
The kelvin is defined as the fraction 1⁄273.16 of the thermodynamic temperature of the triple point of water (exactly 0.01 °C), but change could be ahead in this previously accepted definition which has been in force for more than 50 years.
Here, Graham Machin, Head of Temperature Standards at the National Physical Laboratory (NPL), explains the changes ahead for all temperature measurement – including those at cryogenic temperatures – as the kelvin is redefined in 2018.
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