What is a Magnetic Compass, its principle, types and errors?

Monitoring Compass Performance

Compass performance should be monitored by frequently recording deviations in the compass deviation book. Compass errors should be determined after every large alteration of course, and at least once every watch when there have been no major course alterations. Checking the compass deviation regularly may show the need for repair, testing or adjustment. In addition, compasses should be inspected occasionally by a competent officer or compass adjuster.

 Can we use magnetic compass at the pole?

No, we cannot use magnetic compass at pole  because at the pole the directive force is Zero. At the equator the magnetic compass is more accurate.