Errors of magnetic compass:-
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VARIATION
The true North Pole and the magnetic north pole are not located at the same spot. This variation causes a magnetic compass needle to point more or less away from true north. The amount the needle is offset is called variation because the amount varies at different points on Earth’s surface. Even in the same locality variation usually does not remain constant, but increases or decreases at a certain known rate annually.
The variation for any given locality, together with the amount of annual increase or decrease, is shown on the compass rose of the chart for that particular locality.
Remember: If the annual variation is an increase, you add; if it is a decrease, you subtract
