Definition of Altimeter

An altimeter or altitude meter is a special barometer that can measure the height of a place according to the sea level.

Altimeter versus Barometer

While the barometers indicate the pressure in millimetre (mm) of mercury pressure; altimeters, on the other hand, show the pressure in terms of height directly in meters. From the sea level, the barometer shows a drop of 1 mm of mercury pressure as it goes up in every 10.5 meters.  The table below shows the changes in pressure in accordance with height.

How do altimeters work

The pressure on the top of a mountain and the pressure on its top are not the same meaning that the pressure on the top is less. If the altimeter indicates 800 meters, the altitude of that place is 800 meters from sea level.

As the atmospheric pressure changes less than 0.1 % depending on the humidity and temperature of the air, it is expected that the error that can be made when measuring altitude with altimeter is less than 0.1%.

Pressure Rates

Altitude above sea level Change in Pressure
0 – 700 meters  1 mm of mercury in every 10.5 meters
700 – 1400 meters 1 mm of mercury in every 12 meters
1400 – 2000 meters 1 mm of mercury in every 13 meters
2000 – 2600 meters 1 mm of mercury in every 14 meters
2600 – 3100 meters 1 mm of mercury in every 15 meters
3100 – 3600 meters 1 mm of mercury in every 16 meters
3600 – 4100 meters 1 mm of mercury in every 17 meters
4100 – 4500 meters 1 mm of mercury in every 18 meters
4500-4900 m 1 mm of mercury in every 19 meters
4900-5000 m 1 mm of mercury in every 20 meters

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