altitude datum

altitude datum

[′al·tə‚tüd ‚dad·əm]

(engineering)

The arbitrary level from which heights are reckoned.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

altitude datum

The arbitrary level from which vertical displacement is measured. The datum for height measurement is the terrain directly below the aircraft or some specified datum; for pressure altitude, the level at which the atmospheric pressure is 1013.2 hectopascals/millibars (29.92 in or 760 mm of mercury); and for true altitude, mean sea level.

An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved