I read in a magazine recently about an incident where radio equipment had interfered with the magnetic compass and decided to check things out in my local marina. It was not easy to find information as to how far the equipment should be mounted from the compass; there was no plate on the equipment, but in one case the manual did say at least 1m away. A number of boats had radio equipment fitted closer than this.
Marine equipment is generally supplied with information on compass safe distances contained on notices or in manuals, if not on a plate. These should be referred to if fitting electrical equipment or compasses.
Particular care should be taken if non-marine equipment is fitted e.g. car audio equipment, which will not be supplied with compasses in mind!