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The reference value for P b for b = 0 is the defined sea level value, P 0 = 101 325 Pa or 29.92126 inHg. Values of P b of b = 1 through b = 6 are obtained from the application of the appropriate member of the pair equations 1 and 2 for the case when h = h b+1. [2]
The graph on the right above was developed for a temperature of 15 °C and a relative humidity of 0%. At low altitudes above sea level, the pressure decreases by about 1.2 kPa (12 hPa) for every 100 metres. For higher altitudes within the troposphere, the following equation (the barometric formula) relates atmospheric pressure p to altitude h:
Old altimeters were typically limited to displaying the altitude when set between 950 mb and 1030 mb. Standard pressure, the baseline used universally, is 1013.25 hectopascals (hPa), which is equivalent to 1013.25 mb or 29.92 inches of mercury (inHg). This setting is equivalent to the atmospheric pressure at mean sea level (MSL) in the ISA
Comparison of a graph of International Standard Atmosphere temperature and pressure and approximate altitudes of various objects and successful stratospheric jumps The International Standard Atmosphere ( ISA ) is a static atmospheric model of how the pressure , temperature , density , and viscosity of the Earth's atmosphere change over a wide ...
Thus the standard consists of a tabulation of values at various altitudes, plus some formulas by which those values were derived. To allow modeling conditions below mean sea level , the troposphere is actually extended to −2,000 feet (−610 m), where the temperature is 66.1 °F (18.9 °C), pressure is 15.79 pounds per square inch (108,900 Pa ...
The pascal (Pa) or kilopascal (kPa) as a unit of pressure measurement is widely used throughout the world and has largely replaced the pounds per square inch (psi) unit, except in some countries that still use the imperial measurement system or the US customary system, including the United States.
1–10 kPa Typical explosion peak overpressure needed to break glass windows (approximate) [40] 2 kPa Pressure of popping popcorn (very approximate) [41] [42] 2.6 kPa 0.38 psi Pressure at which water boils at room temperature (22 °C) (20 mmHg) [43] 5 kPa 0.8 psi Blood pressure fluctuation (40 mmHg) between heartbeats for a typical healthy ...
Inch of mercury (inHg and ″Hg) is a non-SI unit of measurement for pressure. It is used for barometric pressure in weather reports , refrigeration and aviation in the United States . It is the pressure exerted by a column of mercury 1 inch (25.4 mm) in height at the standard acceleration of gravity .