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 its 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 altitude - support for the iPad multitasking (split view..)