Indicated altitude in feet (altimeter set to local QNH).
Current altimeter setting (QNH) in inches of mercury.
Outside air temperature in degrees Celsius.
OptionalstationElevationFt: numberElevation of the station providing the altimeter setting, in feet MSL. When provided, the temperature correction is applied only to the altitude above this elevation.
True altitude above MSL in feet.
Computes true altitude from indicated altitude, altimeter setting, and outside air temperature. True altitude is the actual height above mean sea level, corrected for non-standard temperature.
A barometric altimeter assumes the ISA temperature profile when converting pressure to altitude. When the actual temperature deviates from ISA, the pressure levels are displaced vertically and the indicated altitude diverges from the true altitude. This function corrects for that displacement.
When
stationElevationFtis provided, the temperature correction is applied only to the altitude above the station. The air column below the station does not contribute to altimeter error, so restricting the correction to the measured column produces a more accurate result.When
stationElevationFtis omitted, the correction ratio is applied to the full indicated altitude, which matches the standard E6B flight computer method.