This Altimeter determines the height using a digital elevation model. ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) provides digital elevation data with an accuracy of ±10m. Alternatively, you can also only use GPS for height determination. The GPS altitude is less accurate. ASTER only delivers the topographical elevation. Example: When ballooning, ASTER does not provide the height of the balloon, but the elevation of the underlying ground. Peak data provided by peakhunter.com. Features: - Altimeter GPS or ASTER - Apple maps with summits - Summit search - Compass - Distance Grid - Switch between meters and feet