Silva 85E Flush Mount Compass with Illumination

Hi Warren, The below is from the Silva manual which I hope helps COMPENSATION AND DEVIATION Compensation is recommended, if the deviation is more than 5 degrees, when the compass is in its normal mounting position. If the error is less than 5 degrees, it is sufficient to produce a deviation table. The compensation is made with the loose bar magnets to reduce the errors caused by iron objects or other sources of magnetic disturbance. When compensating with loose magnets, a professional compass adjuster ought to be employed. As the magnetic conditions in a boat are liable to change, we recommend checking of the compass once a year and always after installation of equipment which might affect the compass. NB! Do not regard the compass as an accurate navigational instrument until the compensation is carried out and the deviation table is produced. Whenever in doubt, please seek the advice of a compass adjuster! Regards David Shilling