Chapter 1- Diving Equipment Diving Equipment 21 An electronic dive computer is an instrument that provides a digital display of several or all of the following items of information: • Current depth • Maximum depth • Elapsed underwater time • Surface interval • Temperature • No-decompression time remaining • Dive time remaining based on air supply and calculated consumption rate • Cylinder gas pressure • Repetitive group designation • Ascent rate • Dive number • Dive profile • Time to fly • Scrolling (Displaying in sequence the no-decompression limits for various depths for repetitive dives). • Ceiling (Decompression stop depth) • Battery level • Dive planning features Electronic dive computers are the “ultimate instrument” for diving activities. Some computers merely combine information that would usually require several instruments and present the information in a single digital display. Others are decompression computers that continuously calculate nitrogen pressure and ingassing and offgassing in various tissue models. These computers may allow longer dive times because they compensate for time spent at varying depths throughout a dive compared to the “square” dive profiles required for the use of most tables. When dive computers were first introduced in the market some encouraged their use only as a back-up for dives planned according to the NAUI dive tables. This is inconsistent with the purpose of a diving computer, which provides information based on multi-level diving (dives at more than one depth level) computations, not on the “total time at the maximum depth” calculations of the dive tables. Limiting a dive to the dive table time limits does not take advantage of the computer’s capabilities. For a particular profile, dive tables might specify that decompression is required, while the dive computer might indicate no decompression is required due to multi-level calculations. Most dive computers can be used for decompression diving; however, it is recommended that they be used within the computer’s no-decompression limits. The use of computers is not a substitute for proper decompression training and planning and should not be blindly followed. The devices should be used in such a way that any ceiling is avoided at any time during a dive (figure 1-19). This allows a direct ascent to the surface in case of emergency. Dive computers have a range of ascent rates that may be different than the former US Navy ascent rate of 18 m (60 ft) per minute or the current NAUI recommendation of 9 m (30 ft) per minute. Most models have indicators that display ascent rate violations to the diver (figure 1-20). The ascent rate is an important part of the decompression program and must not be violated. Some models of dive computers have dive planning features, which allow the user to plan dive profiles before the dive is made. Another desirable feature of many dive computers is the log mode (figure 1-21). This display shows the essential information from one or more previous dives, and it allows the user to transfer the information to the logbook. Some models store many hours and many numbers of dives that can be recalled, or even downloaded into a personal computer. Many computer programs have time to fly indicators (figure 1-22). These times for various models can vary widely from the traditional 12/24 hour rule, and users should plan accordingly when planning to fly after diving. Consult your dive computer’s owner manual. Since it is not practical to dive according to the tables when using a decompression computer, divers using computers must understand the devices and use them properly (figure 1-23). A pressure transducer in the decompression computer produces a signal which is changed from analog to digital by the Analog-to-Digital (A/D) converter. A microprocessor reads the digital transducer signal, makes calculations, and controls the display. The Read Only Memory (ROM) contains the program for the microprocessor, and the Random Access
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