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.

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).