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Standard sea-level conditions (SSL), [1] also known as sea-level standard (SLS), defines a set of atmospheric conditions for physical calculations. The term "standard sea level " is used to indicate that values of properties are to be taken to be the same as those standard at sea level, and is done to define values for use in general calculations.
This is in contrast to mean sea-level pressure, which involves the extrapolation of pressure to sea level for locations above or below sea level. The average pressure at mean sea level in the International Standard Atmosphere is 1,013.25 hPa, or 1 atmosphere (atm), or 29.92 inches of mercury.
Thus the standard consists of a tabulation of values at various altitudes, plus some formulas by which those values were derived. To accommodate the lowest points on Earth, the model starts at a base geopotential altitude of 610 meters (2,000 ft) below sea level, with standard temperature set at 19 °C.
The standard atmosphere (symbol: atm) is a unit of pressure defined as 101 325 Pa. It is sometimes used as a reference pressure or standard pressure . It is approximately equal to Earth 's average atmospheric pressure at sea level .
Standard temperature and pressure ... At standard mean sea level it specifies a temperature of 15 °C (59 °F), pressure of 101,325 pascals (14.6959 psi) ...
This reference can be the mean sea level pressure , the pressure at a nearby surface airport (QFE), or the "standard pressure level" of 1,013.25 hectopascals (29.92 inches of mercury) which gives pressure altitude and is used to maintain one of the standard flight levels.
the vertical pressure variation, which relates pressure, density and geopotential altitude (using a standard pressure of 101,325 pascals (14.696 psi) at mean sea level as a boundary condition): =, and. the ideal gas law in molar form, which relates pressure, density, and temperature:
The global MSL is a type of vertical datum – a standardised geodetic datum – that is used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and, consequently, aircraft flight levels.