LaDroid compass: a compass aligns itself to point to the magnetic pole.
In mobile phones and other devices using a 3-axis electronic compass, a ∞/8/S shaped
movement is used to calibrate the magnetometer.
For further information about calibration please refer to: http://www.s3sensor.com/en/s3/calibration/recalibrate/index.html
Available for Android 2.3.3+ (rev.10) version.