Celsius

The Celsius scale (also known as centigrade) is a temperature scale named after the Swedish astronomer Anders Celsius (1701-1744), who developed a similar scale. From 1744 until 1954 0°C was defined as the freezing point of water and 100°C as the boiling point (at standard atmospheric pressure).

Kelvin

The Kelvin scale is a thermodynamic (absolute) temperature scale referenced to absolute zero. The kelvin is a unit of measurement for temperature. Both are named after the Belfast-born engineer and physicist William Thomson, 1st Baron Kelvin (1824-1907), who in 1848 whote of the need for an "absolute thermometric scale". The freezing point of water is set at 273.15K and the boiling point at 373.1339K.