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Atmospheric pressure (QFE, QFF, QNH)

Atmospheric pressure is the weight of the air column exerted at the earth's surface or acting on a body, it depends on altitude and weather.

To compare the atmospheric pressure (QFE) measured in different locations with one another (for example, on a map), the values must be "reduced" to standard altitudes. Based on the recommendations of the World Meteorological Organization (WMO), pressure is reduced to sea-level only at stations at an altitude of less than 600 metres. Stations at higher altitudes, on the other hand, are reduced to the meteorological standard pressure surfaces of 850 or 700 hectopascals.

When reducing to sea-level, the (hypothetical) density of the atmosphere between station altitude and sea-level must be assumed. It is standard meteorological practice to automatically factor in the temperature measured at the station. The resulting atmospheric pressure value at sea-level is called the QFF. The currently prevailing humidity is not included in the calculations in Switzerland.

In aviation, the station pressure is reduced independently of the current weather conditions at sea-level. The vertical distribution is uniform according to the ICAO standard atmosphere and the resulting atmospheric pressure value adjusted to sea-level is called the QNH."

Enlargement: PTB330 digital measuring device for determining atmospheric pressure.
PTB330 digital measuring device for determining atmospheric pressure.

The atmospheric pressure is measured using a digital pressure measuring device produced by Vaisala. The devices stand out thanks to their high level of stability and precision. The PTB330 is delivered with three redundant BAROCAP® sensors, which guarantee high-quality measurements and outstanding reliability.