My Elevations uses GPS signals to determine your current location, altitude (elevation above sea level) in both meters and feet, barometric pressure and whether information.
By default, it uses device sensor to determine the altitude, but you also have the option to use elevation api to get the altitude of any other location. On newer devices, using device sensor is more accurate.
It also allows you to get a capture picture and get from gallery of where you are and save it in photo album. Picture will be sealed with coordinates of current location along with altitude and local date/time.
Barometric Pressure is calculated based on elevation. On newer devices such as iPhone 6/6+ value is being delivered directly from device built-in barometric sensor.