Magnetic axis: The hypothetical line connecting the two geomagnetic poles is called the terrestrial magnetic axis. It is the straight line joining the two poles of a magnet (as the magnetic poles of the earth). It is a line through the center of a magnet such that the torque exerted on the magnet by a magnetic field in the direction of this line equals 0.
It is the line connecting the poles of a magnet. It does now not typically coincide exactly with any symmetrical axis of determine. In such instances, a blunder is brought into the indications of the needle which ought to be decided and allowed for in compasses. To decide it with a magnetic needle the suspension cup is made detachable, in order that the needle can be reversed. Readings are enthusiastic about one aspect of the needle and then with the opposite side of the needle up, and the average corresponds to the location of the magnetic axis in both positions of the needle.