This app is a useful tool for Amateur Radio Direction Finding (a.k.a. Fox Hunting), where 5 radio transmitters are hidden in a relatively large area, and the "hunter" needs to locate the "foxes" (transmitters).
The "hunter" aquires the bearing of a transmitter by a special radio receiver, and aims the phone to that direction. The direction can be stored with the plus button. After several measurements, the approximate location of the "foxes" can be found.