Plain English Meaning

Turning the small knob on the altimeter to dial in the current local pressure number so the instrument reads the right height above sea level. Below 18,000 feet you use the local number from a nearby airport or weather station; at and above 18,000 feet, everyone uses the same standard number (29.92).

Full Definition

The procedure of adjusting an aircraft's altimeter to the current local altimeter setting (the station pressure reduced to sea level, expressed in inches of mercury or hectopascals) so that the instrument displays the correct altitude above mean sea level. Pilots are required to set the altimeter to the current reported setting of a station along the and within 100 of the aircraft, or, if no such station is , to the current reported setting of an appropriate available station. When flying at or above 18,000 feet , the altimeter is set to the standard of .