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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 .
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
A below-sea-level surface pressure record of 1,081.8 hPa (31.95 inHg) was set on 21 February 1961. [13] The lowest non-tornadic atmospheric pressure ever measured was 870 hPa (0.858 atm; 25.69 inHg), set on 12 October 1979, during Typhoon Tip in the western Pacific Ocean. The measurement was based on an instrumental observation made from a ...
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 altimeter setting used is the ISA sea level pressure of 1013 hPa or 29.92 inHg. The actual surface pressure will vary from this at different locations and times. Therefore, by using a standard pressure setting, every aircraft has the same altimeter setting, and vertical clearance can be maintained during cruise flight. [1]
TA [3] - Transition Altitude - altitude at which the pilot changes the aircraft's altimeter setting (usually from QNH) to standard pressure (1013.25 hPa) TL - Transition Level - the lowest flight level available for use above the transition altitude; TLY - Transition Layer - the airspace between the transition altitude and the transition level
10 kPa 1.5 psi Pressure increase per meter of a water column [26]: 10 kPa 1.5 psi Decrease in air pressure when going from Earth sea level to 1000 m elevation [citation needed]
The new low south of the main low strengthened quickly, and its central pressure dropped to 982 hPa (29.00 inHg). During the evening of 9 January, the main cyclone to the north continued to bomb out, with a central pressure down to 958 hPa (28.29 inHg). Soon afterwards, it absorbed the deepening low to its south and this merger caused a period ...