Degausser / Demagnetizer
Has your compass gone out of range?
Here are a few causes of compass failure:
The Copter was put on the hood of the car
A flight near a Power line closer than 50 meters
Standing the Copter next to the magnet
How can you fix it?
Buy Any of these
Put it next to Compass and press the Button if it has one.
After 7 seconds compass will be Reset
Go out to the field area and perform compass calibration according to your instructions.