The compass needle will only align itself with the magnetic meridian if it is free from all other influences except the magnetic field of earth.

This is rarely so, particularly on a ship which constructed on steel. The magnetism induced in the steel by the earths magnetic field causes the compass needle to deviate from the magnetic meridian, by an amount which is called the DEVIATION.

A compass by itself is insufficient to indicate position of a vessel. Your compass merely aligns itself with the lines of magnetic force at your location, and from this, and a knowledge of the deviation of these local lines from true, you will have an indication of the North direction.

You may find the local deviation by comparing your compass north with the position of the Sun at local noon. NOT the time zone noon!

If you are lying off some land features that you can identify on the chart, then by taking cross bearings to a few of these, your position may be deduced.