Chapter 1- Diving Equipment Diving Equipment 23 to offgas completely. Dive buddies may not share a single computer. Each diver relying on a computer for dive planning and no-decompression status must be equipped with a dive computer. Electronic dive computers require considerable care and maintenance. Prevent shock, extreme heat, proximity to magnetic fields, etc. Dive computers are not damaged by reduced pressure at higher elevations. In fact, some computers adjust for reduced atmospheric pressure and function correctly for altitude diving. Rinse your computer well after every use. Carefully follow battery replacement procedures. Your computer will provide ample warning when replacement of batteries is needed. Many models require periodic maintenance and calibration checks. A computer can make diving easier and allow you to spend more time underwater than conventional dive tables. You must, however, use your dive computer wisely and properly. Be sure to read the manual provided with your dive computer and take a course to learn about its operation. See the chapter on “Decompression” for more information on dive planning with a computer. Diving Compasses A freely suspended magnet tends to align itself with the magnetic field created by the earth, which acts as a large magnet. This principle is the basis for a valuable reference device called a compass. Special compasses designed to withstand the environment are available for diving and are extremely useful reference instruments (figure 1-24). Diving compasses are either dry or liquid-filled. The preferred type of compass for diving is liquid-filled. This type consists of a magnetic disc or arrow called a compass card that rests on a bearing under its centerpoint. Incorporated into the card is a float that minimizes the weight of the card on the bearing. Well-constructed liquid filled compasses can correctly indicate direction even when tilted considerably from a level position. The liquid also serves to dampen the movement of the arrow or compass card, which makes the instrument easy to use. FIGURE 1-24. DIVING COMPASS Since the instrument is full of liquid, it is unaffected by pressures encountered at depth. A dry compass construction is similar to that of a liquid-filled compass, but the compass card does not have a float assembly and must be lighter in weight. This type of compass is less expensive than the liquid-filled compass. A dry compass, however, is less accurate; the card tends to oscillate (swing back and forth) and is subject to the effects of pressure. A compass merits the same treatment that should be given to all diving instruments. Rinse it well after use, giving particular care to the bezel (rotating collar). Prevent shock and prolonged exposure to sunlight and high temperatures. Heat will cause the liquid in a liquid-filled compass to expand and cause leakage. Recalibration of compasses is not required. Sonar navigation devices use a transmitter that is placed by the diver or boat operator and a diver-worn receiver that detects the transmitter’s sonar signals. Use of diving compasses and sonar navigation are described in the Navigation chapter in the Diving Techniques section of this book. Buoyancy Systems There are many types, designs, and features of buoyancy compensators (BCs). The three basic types are called horsecollar, jacket, or back inflation units.
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