This app uses the built in barometric air pressure sensor of the iPhone 6, iPhone 6 Plus and iPad Air 2.
It will locate your geographic position and calculate your altitude in feet and meter above the main sea level. The correct absolute air pressure is given by the Weather service and the relative air pressure is given by your device sensor.
Extendable you can save your actual data with your level, city and timestamp to the history.
Only the iPhone 6, iPhone 6 Plus and iPad Air 2 will give you the whole functions of this app.