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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
The barometric formula is a formula used to model how the pressure (or density) of the air changes with altitude. ... P 0 = 101 325 Pa or 29.92126 inHg.
BS 1042:1:1964 notes that the "conventional pressure of 30 inHg is based on the conventional density of mercury (13.5951 g/cm 2) at 0 o C" but also lists a reference pressure of 30 inHg that was "the pressure due to a 30 inch column of mercury at 60 o F under an acceleration of free fall of 32.1740 ft/s 2" adding "This reference unit of ...
[1] [2] [a] It is denoted mmHg [3] or mm Hg. [ 4 ] [ 2 ] Although not an SI unit, the millimetre of mercury is still often encountered in some fields; for example, it is still widely used in medicine , as demonstrated for example in the medical literature indexed in PubMed . [ 5 ]
Atmospheric pressure, also known as air pressure or barometric pressure (after the barometer), is the pressure within the atmosphere of Earth.The standard atmosphere (symbol: atm) is a unit of pressure defined as 101,325 Pa (1,013.25 hPa), which is equivalent to 1,013.25 millibars, [1] 760 mm Hg, 29.9212 inches Hg, or 14.696 psi. [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]
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.