Computers

What to Look for in a Dive Computer

There are three very good reasons to purchase a quality dive computer. Firstly, used properly, a dive computer will greatly increase diver safety by reducing the risk of decompression sickness. They do this by calculating complex decompression algorithms and provide the diver with the best possible information. Ideally, the computer should have three modes: air, nitrox and gauge.The Air mode should accommodate for use with standard air only, the Nitrox mode for use with up to three nitrox mixes containing 21-99% oxygen and the Gauge mode for use as a simple bottom-timer.

The second reason to own a good dive computer is because they do all the complex calculations, you are free to concentrate on your diving, which will make your time under the water more enjoyable.

The third and final reason to invest in a good quality dive computer is because they give you more bottom time with increased safety.

There are four vital safety elements to consider when choosing a computer.

1. Does it use microbubble technology to calculate decompression?

2. Does it offer continuous decompression?

3. Does it offer a multi-step ascent rate?

4. What about personal adjustment?

Why is RGBM so important?

The traditional approach to decompression theory is referred to as multi-tissue, based upon the research of the pioneer of diving medicine, Professor J S Haldane. Despite the fact that his research is over 100 years old, it is still the basis for the most commonly used dive tables such as the US Navy and Bhulmann, and thus the basis for most dive computers today. These traditional tables break the body into sections, which can absorb and eliminate nitrogen at different rates. These are called tissue compartments. (eg blood, bone, muscles and organs). Modern research by Suunto and the renowned Bruce R. Wienke has shown a different approach significantly improves diver safety. The now famous Doppler testing found that micro-bubbles exist in our body when we dive. The key to avoiding decompression sickness is to keep the bubbles small enough so that they can travel through all tissue compartments.

The Reduced Gradient Bubble Model, the most advanced table available to minimize growth of micro-bubbles is the safest system available.

What about ascent rate?

Many companies still use outdated variable ascent rates, ie: the computer allows you to ascend faster at deeper depths. More recent testing and research by Suunto has established a slower ascent rate. This offers both a greater chance of eliminating micro-bubbles of nitrogen through normal exchange in the lungs, and less chance of these bubbles reaching a damaging size. As a result of extensive research, Suunto has applied the principle of a single slow ascent rate of 10 metres/min. In order to aid in maintaining a slow ascent rate Suunto uses a multi-step ascent rate meter on all models.

Calculating Decompression

The most accurate method of calculating decompression is by using the Suunto RGBM. The Suunto RGBM (Reduced Gradient Bubble Model) is used in the Vyper, Stinger, Vytec, Mosquito and the Cobra models of dive computer.

In essence, the Suunto RGBM is an advanced algorithm for tracking both dissolved and free gas in the blood and tissues of divers. The advantage of the Suunto RGBM is that it can address a number of diving circumstances outside the range of just-dissolved gas models by, for example, monitoring continuous multi-day diving, computing closely spaced repetitive diving and taking into account adverse dives deeper than the previous dive.

Continuous Decompression

Continuous decompression is the ability to measure and calculate, in real time, the optimum depth for decompression. Since the calculation is updated at very short intervals, the diver is guided to the surface in numerous short stops. The sets of ideal decompression depths tend towards an exponential curve, which represents the function governing tissue nitrogen absorption and elimination. Combined with a controlled ascent rate, it is one of the most natural decompression methods known today.

What else?

Other desirable features to consider are: safety stop countdown, preset alarms with automatic backlight activation, adjustable profile memory sampling rate and bookmarks. And of course it should be a very good watch, incorporating complete calendar clock functions, dual time, daily alarm and a stopwatch with elapsed time and split-time measurement. The ability to create personal settings through adjustment options give more versatility and safety to the diver.

The Cobra, Mosquito, Stinger, Vyper and the Vytec feature a high-definition electroluminescent display which can be adjusted to be on for 5 to 30 seconds, or turn on automatically when an important alarm is given.

Finally, most of the top line models offer a feature that they call The Interactive Advisory System. Most of the top line computers offer this feature which is an intuitive menu system much like a mobile phone read-out. It makes life substantially easier.

Can I interface my dive computer with my PC?

Being able to download dive profiles is becoming increasingly popular among divers. Suunto introduced the first PC interface in 1989 and has held the lead in this area ever since. The large memory capacity of the Suunto dive computers allows you to transfer data ó dive profile, maximum depth, temperatures, air consumption and nitrox information ó directly from your dive computer to your PC at home or your laptop on board.

What about memory?

Memory is important. You’ll need to choose a computer with sufficient memory to cover you for your dive period. All of the computers in the following pages have logbook and history memory. However, the Spyder, Cobra, Vyper, Mosquito, Stinger and Vytec store up to 36 hours of detailed dive information that can be either viewed on the screen, or downloaded to your PC. In fact, some of these computers even allow you to set the sampling rate (the interval it takes a reading, either 60, 30, 20 or 10 seconds).