The Celsius and Fahrenheit scales
Three temperature scales are in common use: the Celsius, Fahrenheit and Kelvin scales.
Fixed points
The unchanging temperatures used to set up a temperature scale are its fixed points: the melting point of pure ice and the temperature at which water turns to steam, both at a pressure of one atmosphere.
They were chosen because they are easy to reach and do not change, except with pressure.
| Scale | Ice melts | Water boils | Divisions between |
|---|---|---|---|
| Celsius | 0 °C | 100 °C | 100 |
| Fahrenheit | 32 °F | 212 °F | 180 |