This educational app lets you explore magnetic fields with your iPhone 3GS.Imagine your phone's magnetic sensor as a small magnet. Other than a usual compass, it can rotate freely in all directions. This lets you explore the direction of the earth's magnetic field in 3D. To let you see the angle of incidence better, the app shows a thin stick pointing up and down together with the magnet. You can also test the effect of other magnets close to the phone, but be aware that the sensor is quite sensitive and easily reaches its limits. If that happens and the small display shows 'Out of Range !', move the magnet further away. If the magnet seems stuck after that or behaves strangely, shake the phone to recalibrate the sensor.