Pressure Altimeter uses a built-in barometric pressure sensor in your device to calculate precise altitude above sea level. It is more reliable than a GPS receiver for measuring altitude in case the GPS signal is not available. The pressure Altimeter can be used for any outdoor and indoor activities such a hiking, mountain climbing, or even elavator ride to meassure the height of a building.Barometric pressure changes with the weather, and for that reason the app downloads weather data from the nearest meteorological station to calibrate the barometric sensor.