Proper care and feeding of a magnetic compass is a subject that lends itself to some study. How to apply magnetic compass readings to charts correcting for true vs. magnetic North, even with a properly installed compass with a properly achieved deviation table is a formula based on your location latitude and longitude wise and your particular installation and being in possession of proper nautical charts.
Navigation based on compass points has been reduced to an "ancient" art as most "modern" navigators, especially pleasure boaters, utilize chart plotting GPS units and don't know a thing about compass navigation, don't own the charts to make a compass of much use and don't intend to have parallels or dividers on board either. Great suggestion for a thread "Where do you stow your Sextant on your RIB"
I don't know about the Royal Navy but the U.S. Navy abandoned Sextant Navigation training at the Navel acadamy a couple of years ago and now teaches only "Electronic" Navigation.
Forget the compass, bust for a chart plotting GPS if you travel in places where you lose visual reference to landmass and have a nice day.