Scuba – The Dive Computer
The computer revolution of the 1980s that led to ever smaller PCs was not a boon only to business. Scubadivers, too, have benefited enthusiastically from the electronics and miniaturization advances.
A dive computer is a wristwatch (or in this case, even a mask) -like device that measures time and ambient pressure, temperature and sometimes other variables. Its primary purpose is to make measurements and calculations that provide the diver with recommendations for safe ascent. With a dive computer strapped on, the chances of suffering decompression sickness – the bends – is drastically reduced.
A dive computer will display the safe rate of ascent based on estimates of the amount of nitrogen absorbed during the dive. It does this by a combination of direct measurement of ambient pressure and time, along with a calculated depth and in-built algorithms about nitrogen absorption.
Turning the computer on during travel to the dive is helpful so that it can measure the conditions the diver experiences before entering the water.
Dive computers are available in a wide price range, and in general the more expensive have more functions. Some measure just the basics, others can actually measure tank pressure and even gas mixture.
Several models will take and store measurements and calculations, then allow for downloading to a PC so the dive can be analyzed at home. That allows knowledgeable divers to tailor future dives for more efficient use of dive time, while still retaining a wide safety margin.
Some dive computers will even provide divers with post-dive recommendations about when it's safe to fly again. Airplane cabins contain pressurized air. That affects the rate at which nitrogen – absorbed into the lungs and bloodstream – will be safely released back out of solution and exhaled. Decompression sickness can occur anywhere from immediately to several hours after completing a dive.
Most dive computers calculate and recommend based on 'open circuit' systems in which the diver breaths from a 2-stage regulator attached to a tank and standard face mask, exhaling into the regulator and inhalation tube.
Some air systems are closed-circuit, sometimes called 'rebreathers'. These air supply systems allow divers to rebreath 'scrubbed' air. The exhalation is filtered to remove CO2. Since inhaling air with 21% oxygen produces 18% oxygen and 3% CO2, such systems can be very efficient. There are dive computers available for use with closed-circuit systems. Make sure you know which you're getting.
The majority of dive computers have menus and the owner should become familiar with the device topside. It's particularly helpful to practice under simulated conditions. So, after gaining basic familiarity with how to operate it, try doing the same in a tub of water, with the bathroom lights dimmed.
Good diving practice mandates that you 'plan your dive and dive your plan'. In this case, that means using your computer to help plan your dive, then following its recommendations during the dive, unless an emergency requires you to abandon it.
However, remember that dive computers have in-built programming that is based on assumptions about how gases are absorbed and released. But no two divers are exactly alike. The dive computers display gives recommendations. Never abandon common sense and err on the side of your safety.