Bar (unit)
The bar is a metric unit of pressure, but not part of the International System of Units (SI). It is exactly equal to 100000 Pa and is slightly less than the average atmospheric pressure on Earth at sea level.
The bar and the millibar were introduced by the Norwegian meteorologist Bjerknes, who was a founder of the modern practice of weather forecasting.
Use of the bar is deprecated by some bodies in some fields. The BIPM lists it as one of the "non-SI units [that authors] should have the freedom to use" but does not include it among the "Non-SI units accepted for use with the SI",. The NIST deprecates its use in the US except for "limited use in metrology" and lists it as one of several units that "must not be introduced in fields where they are not presently used." The IAU also lists it under "Non-SI units and symbols whose continued use is deprecated." As of 2004, the bar is legally recognized in countries of the European Union.
Units derived from the bar include the megabar (symbol: Mbar), kilobar (symbol: kbar), decibar (symbol: dbar), centibar (symbol: cbar), and millibar (symbol: mbar or mb). The notation bar(g), though deprecated by various bodies, represents gauge pressure, i.e., pressure in bars above ambient or atmospheric pressure.
The bar is defined using the SI unit pascal, namely: 1 bar ≡ 100000 Pa. 1 bar is therefore equal to:
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