Altitude

The vertical distance of a level, a point or an object considered as a point measured in feet Above Ground Level (AGL) or from Mean Sea Level (MSL). 1) MSL Altitude. Altitude expressed in feet measured from mean sea level. 2) AGL Altitude. Altitude expressed in feet measured above ground level. 3) Indicated Altitude. The altitude as shown by an altimeter. On a pressure or barometric altimeter it is altitude as shown uncorrected for instrument error and uncompensated for variation from standard atmospheric conditions. (FAA4)