The compass uses the action of the earth's magnetic field to indicate the north. It uses the principle that the magnetic field is repelled by the same polarity and the opposite polarity is attracted. Then, the north is used as the starting point, and it is set to zero degree. The clockwise direction is determined in order. , can be used to indicate the direction. Positioning must match the use of the map to find the relative position to understand where it is. Note that the north of the compass is not true north, but magnetic north. This is because the south, north, and geomagnetic south and north poles of the earth are not in one position, but have an angle. This angle is called magnetic declination. The magnetic declination angles of different locations are generally different, and the magnetic declination of the same location also changes with time.