THE man who discovered that a freely pivoting magnet always swings magnetic north has long been forgotten, but that simple property has been essential to most navigation equipment since.
Because they are so simple, magnetic compasses for divers all cost around £30. Any additional price reflects the way the compass is mounted in a console, and the other instruments it has alongside.
Using a compass is an essential skill for any diver, and it takes only a little practice to become proficient. You must be careful to avoid any interference from the ferrous metal you are wearing such as the steel cylinders on your back, and you should be aware that a magnetic compass is of little use to a diver within the confines of a steel wreck.
Console-mounted models are located at the end of the pressure gauge (SPG) and high pressure hose. With a wrist model, it is usually best to take it off your arm when using it. This makes it easier to hold its "direction of swim" or "lubber" line parallel to your body. In either case be sure to hold it level so that the needle or compass card does not jam. This is sometimes easier said than done underwater, but most compasses listed in the directory have a sighting window, which makes it easy to take a bearing on an object.
There are new electronic compasses now coming on to the market that make it easy to pre-programme a complex route and its reciprocal before setting off. They cost around £100 more than the average compass.
The next navigational aid awaited by divers is a global positioning system that will work under water!