How to define Celsius Scale?
CELSIUS SCALE, the temperature scale commonly used for scientific measurements and the scale used for all purposes in most countries of the world. The Celsius scale, also called the centigrade scale, was long defined on the basis of two fixed points: the freezing point of water, which was assigned a temperature of 0°, and the boiling point of water, which was assigned a temperature of 100°. It is named in honor of Anders Celsius, a Swedish astronomer who first advocated such a scale.
In 1954 the International Committee on Weights and Measures adopted a new basis for the Celsius scale, defining it in terms of the properties of an ideal gas and a single fixed point—the triple point of water. Under the new definition, the boiling and freezing points of water are only reference points, but for most practical purposes the new and the old scales are the same. The Celsius temperature T( °C) and the Fahrenheit temperature t(°F) are related by the expression t = %T + 32.