Here you can buy a compass or a map measurer for your next trip.
A magetic compass measures the Earth's magnetic field. It consists of a suspended magnet that can rotate in the horizontal plane (also called "compass rose"). Due to the magnetic field around the Earth, the magnet will always alligh with its north and south poles and point towards the Earth's magnetic poles. A magnetic compass does not point 100% towards the geographic north but points towards the magnetic north.