This application is using to convert values between Réaumur and Kelvin.

°Ré or Réaumur:

The Réaumur scale (French pronunciation: ​[ʁeomy(ː)ʁ]; °Ré, °Re, °r), also known as the "octogesimal division", is a temperature scale for which the freezing and boiling points of water are defined as 0 and 80 degrees respectively.

The scale is named for René Antoine Ferchault de Réaumur, who first proposed a similar scale in 1730.

The Réaumur scale was used widely in Europe, particularly in France, Germany and Russia, and was referenced in the works of Dostoyevsky, Flaubert, Tolstoy, and Nabokov.

By the 1790s, France chose the Celsius scale for the metric system instead of the Réaumur measurements, but it was used commonly in some parts of Europe until at least the mid-19th century, and in parts of Russia until the early 20th.

Its main modern uses are in some Italian and Swiss factories for measuring milk temperature during cheese production, and in the Netherlands for measuring temperature when cooking sugar syrup for desserts and sweets.

°K or Kelvin:

The Kelvin scale is an absolute thermodynamic temperature scale using as its null point absolute zero, the temperature at which all thermal motion ceases in the classical description of thermodynamics.

The kelvin (symbol: K) is the base unit of temperature in the International System of Units (SI).

Until 2018, the kelvin was defined as the fraction ​1⁄273.16 of the thermodynamic temperature of the triple point of water (exactly 0.01 °C or 32.018 °F).

In other words, it is defined such that the triple point of water is exactly 273.16 K.

On 16 November 2018, a new definition was adopted, in terms of a fixed value of the Boltzmann constant.

For legal metrology purposes, the new definition will officially come into force 20 May 2019 (the 130th anniversary of the Metre Convention).

The Kelvin scale is named after the Belfast-born, Glasgow University engineer and physicist William Thomson, 1st Baron Kelvin (1824–1907), who wrote of the need for an "absolute thermometric scale".

Unlike the degree Fahrenheit and degree Celsius, the kelvin is not referred to or written as a degree.

The kelvin is the primary unit of temperature measurement in the physical sciences, but is often used in conjunction with the degree Celsius, which has the same magnitude.

The definition implies that absolute zero (0 K) is equivalent to −273.15 °C (−459.67 °F).

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