| 1 | # Temperature Scales
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| 3 | **Celsius**, historically known as **centigrade**, is a scale and unit of measurement for temperature. As an SI derived unit, it is used by most countries in the world. It is named after the Swedish astronomer Anders Celsius (1701–1744), who developed a similar temperature scale. The degree Celsius (**°C**) can refer to a specific temperature on the Celsius scale as well as a unit to indicate a temperature interval, a difference between two temperatures or an uncertainty. Before being renamed to honour Anders Celsius in 1948, the unit was called centigrade, from the Latin *centum*, which means 100, and *gradus*, which means steps.
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| 5 | From 1744 until 1954, 0 °C was defined as the freezing point of water and 100 °C was defined as the boiling point of water, both at a pressure of one standard atmosphere with mercury being the working material. Although these defining correlations are commonly taught in schools today, by international agreement the unit "degree Celsius" and the Celsius scale are currently defined by two different temperatures: absolute zero, and the triple point of VSMOW (specially purified water). This definition also precisely relates the Celsius scale to the Kelvin scale, which defines the SI base unit of thermodynamic temperature with symbol K. Absolute zero, the lowest temperature possible, is defined as being precisely 0 K and −273.15 °C. The temperature of the triple point of water is defined as precisely 273.16 K and 0.01 °C.
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| 7 | ## Calculator Example
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| 9 | This simple F-to-C example illustrates how InfoClay documents can be used to *explain* a concept, and then enables the reader to *explore* the explanation by interacting with the calculations, visualizations and simulations presented.
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| 11 | Mathematically, we are performing:
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| 13 | ---
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| 15 | $$
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| 16 | C = \frac{5}{9} (F - 32)
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| 17 | $$
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| 20 | [Enter a Fahrenheit Temperature](:?F|number)
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| 22 | [](:=C=5.0/9.0*F-5.0/9.0*32)
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| 24 | [The Fahrenheit temperature](:!F) *is equivalent to* [the Celsius temperature](:!C)
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| 26 | ---
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| 28 | [Back to Home](:@Home)
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