Setting for pressure altimeters
Altimeter setting is the value of the atmospheric pressure used to adjust the scale of a pressure altimeter so that it indicates the height of an aircraft above a known reference surface. This reference can be the mean sea level pressure (QNH), the pressure at a nearby surface airport (QFE), or the "standard pressure level" of which gives pressure altitude and is used to maintain one of the standard flight levels.
The setting of a sensitive pressure altimeter is shown in the Kollsman window.
The QNH altimeter setting is one of the data included in METAR messages. An alternative setting is QFE or SPS/STD:
QNH and QFE are arbitrary Q codes rather than abbreviations, but the mnemonics "nautical height" (for QNH) and "field elevation" (for QFE) are often used by pilots to distinguish between them.
QNH and QFE will have errors when not at station elevation. QFF is aerodrome pressure (QNH) reduced to sea level. It is designed to read zero at sea level in the vicinity of the aerodrome, unlike QNH which will not read precisely zero at sea-level.
Related to the altimeter settings are: