Kuzma Shapran BubbleCompassFree v1.0 S^3 Anna Belle Signed
A mixture of a Bubble level and a Compass.
The full version also shows magnetic declination and GPS coordinates (when available), displays more data and markers. The magnetic declination can be calculated even if it is not explicitly reported by GPS.
Note: the precision of smartphone sensors usually is not sufficient for industrial, navigational or any other real-life uses.