This altimeter delivers the altitude of your current position either from the device (GPS) or from the ASTER digital elevation model (with a horizontal accuracy of 30m).Depending on your current position and your device one of the two methods is more correct. Using GPS on the device is known for a large error in the altitude for difficult receiver conditions it’s not available for network based positioning at all.Therefore this altimeter works on iPods and iPhones without a GPS sensor.More features:- switch between metric and feet units- set an optional target altitude- switch between Device, ASTER and combined altitudeKeywords: altimeter, gps, nasa, aster, elevation, flight, hiking, outdoor, accurate, earth, position, measure, track