Essential further information for divers
As well as knowing the amount of air in their tank, the three basic pieces of information that divers need to know are: the amount of time they have spent underwater, the depth of the dive and their direction. For this, divers need to time the dive. Divers also need to be able to measure depth and know the maximum depth achieved. Finally, divers need to be able to navigate underwater.
It may be obvious why divers need to navigate, but why do they need to know depth and time? The tissues of the body absorb the nitrogen in the air we breathe underwater. The deeper we go, the greater this effect. We need to be able to calculate the maximum time we can stay at any given depth without ill effect. There are diving tables that give these figures.
Diving watches
A suitable watch is needed to time the dive. It should be waterproof to a maximum depth of at least 100 m (330 feet).
This is not because a diver will go to that depth, but because of a curious system used by watchmakers to calibrate their watches. Divers need watches that are more than just water resistant. A watch that claims to be water resistant to 30 m (100 feet) is great for wearing while washing the car, but it is not good for any other water-related activity. The watchmaker’s code for water resistance relates to static-water testing only and doesn’t mean that a watch is suitable as a diver’s watch.
A diving watch needs to have an omnidirectional bezel that can be used to mark the moment that a diver left the surface. The bezel should move in only one direction so that if it gets accidentally hit it can’t move to a later start time. The watch face should allow you to read the time even when the water clarity is not good. If it breaks underwater, then all you need is a watch repair.
Depth gauges
A depth gauge is as important to a diver as an altimeter is to an air pilot. This instrument is also a navigation tool because it can tell divers if they are travelling up or down through the water column.
A good depth gauge will include a method of recording the maximum depth achieved during the dive.
Compasses
A conventional compass is used underwater in exactly the same way as it is used on land except that a diver has to be sure to hold it in the right way.
A compass has a magnetic pointer that must be allowed to swing. Some compasses have a sight glass to allow you to read off a bearing while holding it up in front of you. Often the depth gauge and compass are included in a single console at the end of a hose together with the tank pressure gauge. The electronic revolution has not only given us watches, both analogue and digital, but we can now equip ourselves with electronic compasses that work underwater, too. One very popular type is combined in a watch-sized diving computer.
