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Buying a Dive Computer

Buying a Dive Computer

A dive computer allows divers to extend their time and safety while in the water. Considered essential by most dive operators around the world today, your dive computer should be one of the first things you should buy.

Since back in the 1980's dive computers have been revolutionising the way that we dive. Before the dive computer came along you would calculate your dive time based on the maximum depth you were diving to. The dive computer changed this significantly by being able to calculate your max dive time based on the actual dive allowing multi-level diving. Modern dive computers update you constantly on how much time you have left, based on your current depth. Essentially this allows you to remain underwater for longer in safety with potentially shorter safety stops.

Shop our dive computers department online.

How Dive Computers Work

Put simply, dive computers use a depth sensor and a timer to work out how fast you absorb gases into your body by using an algorithm inside them. The deeper and longer you stay down the faster you absorb the gases you're breathing and your computer monitors your depth and time at all times.

The Basics

  • Depth – Dive computers will record the depth you are currently at as well as the maximum depth reached on that dive.
  • Time – From the moment you descend most standard Dive Computers log and display the total dive time. Some will calculate your total bottom time as an added feature.
  • Surface Time Interval – Time spent above the water between the previous dive and the start of the current dive.
  • No Decompression Limit – Time limit of when a diver can ascend with no safety stop.
  • Safety Stop – As soon as you hit the required safety stop depth (5m), most standard dive computers will automatically begin count down of 3 minutes.
  • Ascent Rate – If you exceed the maximum ascent rate (ascending faster than 9m/ 30ft per second) you can cause serious injury and increase the chances of decompression sickness. Most standard Dive Computers will beep and warn if you are going faster than this speed.
  • Algorithm – Each brand of Dive Computer works by their individual dive table settings however, they work within the universal RDL diving table whether in Metric or Imperial. It’s important for your safety to read the Dive Computers user manual before use.

Your dive computer keeps you safe and has multiple alarms to let you know if you go down too deep, ascend too fast, or if you have an air integrated computer, which uses an air transmitter to receive your air pressure throughout the dive, it will even tell you how long your air will last.

When you ascend during a dive your computer will automatically go into a safety stop and tell you what depth to stay at and count down how long for. Most computers today alarm when you do something wrong like ascend too fast, or stay down too long, so you can concentrate more on the dive at hand.

Air and Nitrox

Most dive computers today come with Nitrox algorithms so you can swap between air and nitrox. These computers can be set to different levels of O2% and some can even handle multiple values during the same dive if you dive with multiple mixes. Trimix is the next level by adding Helium to the mix and requires further training before you can dive safely on it. If you're thinking of progressing to far deeper depths then a trimix computer is a consideration.

Algorithms

There are various different decompression models coded into hundreds of dive computers around the world that will work out your Nitrogen loading based on your dive profile. They won't all give the same results as one will be more conservative than others, or use a different decompression theory. Because of this if you're diving with a computer different to your buddy, you can be waiting around for them to end a safety stop, or forced to ascend because they are reaching their No Decompression Limit (NDL) faster than you are.

Some dive computer manufacturers have understood the issue of multiple algorithms being used, so they have coded multiple algorithms into their dive computers, and you can choose ones that better match each other. Even if your dive computer doesn't support multiple algorithms, ir most likely will enable you to adjust the conservatism of its algorithm. This can also be used to match your buddy's dive computer so you can match their dive profile better.

Most dive computers will have a conservatism factor that you can change because not all divers are the same. Algorithms are fairly generic and everybody is slightly different when it comes to fitness and body composition, so you can tell some computers to be more or less conservative based on your body, as well as altitude of the dive too.

Suunto RGBM – Reduced Gradient Bubble Model

The Suunto Reduced Gradient Bubble Model (RGBM) is a state of the art algorithm for managing both dissolved gas and free-gas in all its stages in the tissues and blood of the diver. Suunto computers have one of three RGBM models inside, either the standard RGBM which is great for recreational diving, RGBM Technical for deeper advanced diving, and Fused RGBM that combines the two for the best of both.

It is a significant advance on the classical Haldane models, which do not predict free-gas (microbubbles). The advantage of Suunto RGBM is a more accurate representation of what is happening in the diver's body, through its ability to adapt to a wide variety of situations.

The Suunto RGBM addresses a number of diving circumstances that have not been considered by previous dissolved gas models, adapting to:

  • Continuous multiday diving
  • Closely spaced repetitive dives
  • Dives deeper than the previous dive
  • Rapid ascents which produce high microbubble build up

The Suunto RGBM algorithm automatically adapts its predictions of both the effects of micro-bubble build up, and adverse dive profiles in the current dive series. It will further modify these calculations according to the personal adjustment that a diver can select. Essentially when you dive you take on gas, this is called on-gassing. You need to off-gas for a sufficient time during surface intervals to avoid illness. The Suunto RGBM algorithm helps you to do this correctly. Click here to see our range of Suunto Diving Computers.

Screens and Display

Not all displays on dive computers are the same. Entry level computers will have a segmented display much like a digital watch, and can be harder to display complicated information. Dot Matrix screens have lots of small segments that can spell out more complicated information and be easier to understand. Some modern dive computers have colour screens that have far greater detail and intuitive colours, but they do tend to use more battery power, so tend to be rechargeable.

Colour screens are best as the colours draw your eye to important information if you get close to a limit. The LED or LCD backlight for colour screen computers makes them easier to see in low light and poor visibility.

Segmented display computers have a range of symbols outside of the centre that tell you need to read the manual to understand.

PC and Mac Integration

You may want to consider not only logging your dives in your log book, but also on your PC. All major manufacturers now have models that can download your dive data to your PC. This allows you to see your whole dives in profile and provides extra information not normally accessible via the dive computer itself. Some computers are now including the download software and interface, whilst with others you have to purchase them separately.

Right now we're seeing the introduction of dive computers that use Bluetooth connectiveity to let you download you dive computer data.

Wrist or Console Mounted?

The fashion in Australia is for wrist mounted computers. Typically console mounted computers are used by dive centres, dive resorts etc. There are arguments for both systems, but here are a couple of points you should consider before deciding which would suit you best:

Console mounted dive computers are larger and are attached to your regulator via a hose. This makes them less likely to be mislaid. A console mounted dive computer is not necessarily an air integrated dive computer, but many are. The pressure gauge in your console requires a connection to your tank in order to show a pressure reading, but this does not mean that the computer is connected to the air source too. Some dive computers are simply a wrist computer mounted into a console next to a traditional SPG.

Wrist mounted dive computers strap to your arm and are either a large screen or watch sized. Watched size computers can be worn after the dive day to day, but have smaller screens. Large screen computers can be easier to read.

Wrist mounted computers can be used for other purposes such as free diving swimming and other sports. Some computers are solely made for apnea freediving and don't have the same alarms and algorithms as most dive computers. Click here to take a look at our range of dive computers with an Apnea Modes, plus apnea only computers.

Air Integration

With an air integrated dive computer you have another great benefit in that the computer tells you how much air you have left and can calculate your breathing rate, telling you how much time you have left to dive at your current air consumption rate. This facility also allows the computer to monitor and learn your breathing rates so that if the current is behind you and your breathing slows, the computer can rightly calculate that you absorb less nitrogen and therefore you can remain underwater longer.

Air integrated dive computers can either be hosed or hoseless (via a transmitter on the first stage).

Hoseless air integration requires that an appropriate air transmitter is attached to your first stage regulation. We recommend using a short 15 cm (6 inch) high pressure hose to do this, rather than connecting the transmitter directly to the 1st stage regulator.

Alarms

Most dive computers will have visual and audible alarms to warn you when you get close to a limit, such as no stop time approaching, fast ascent etc. You will hear a beeping underwater to tell you to look at your computer and the backlight will flash to draw your attention.

You can also set your own alarms in most computers too, like a dive time alarm that tells you when you've been underwater for x amount of time. A tank pressure alarm on integrated computers is useful so your computer will tell you when you get low on gas. And no decompression limit (NDL) alarms tell you when you get close to your no decompression limit and you have to ascend.

General Safety

There are a few basic considerations with using a dive computer which you should be aware of:
  • Read the instruction manual thoroughly before using the computer so you understand how the computer works and what it's trying to tell you.
  • Never share a dive computer; if one of the buddy pair is not diving on a computer you must abide by your dive tables.
  • Do not 'ride the zero', this is waiting for the no stop time on your dive computer and then ascending a few metres and waiting again to stay underwater longer. Although a dive computer is meant to extend your dive time, this is pushing your luck.
  • Remember, to help avoid decompression illnesses follow the common sense suggestions you learned in training, avoid dehydration, alcohol etc. and that algorithms are generic so you may be in the limits on your computer and still be affected.

Battery Changes

Modern dive computers are often made with user changeable batteries. However, only a few have watertight battery chambers meaning that if you fit the battery wrongly and it floods, the whole computer is ruined. For this reason most divers still return their computers to service centres for battery changes and servicing. Although more expensive than doing it yourself, having professionals do it is much less expensive than a new dive computer.

Most watch style dive computers need the battery changed by a qualified service centre and pressure tested to ensure its waterproof again.

Screen Guards

Screen guards are now fitted on most dive computers to stop the screen getting scratched. These guards will quickly become very scratched and although difficult to read on dry land once submerged the scratches virtually disappear. However if the guard becomes too scratched, or cracked, replacements are available. If your computer does not have a screen guard make sure you purchase a perspex (not stick on) cover for it if available.

Recommended Dive Computers

Entry Level, Large Screen

  • Cressi Leonardo Nitrox Wrist Dive Computer Cressi Leonardo Nitrox Wrist Dive Computer
    RRP: $449, Our Price: $349, You Save $100 (22%).
    For a new diver, plus the experienced recreational diver, the Cressi Leonardo dive computer has got all of the essentials, yet is simple to use and ideal for those who 'just want to dive'. This value for money, dive computer was awarded Scuba Diving ScubaLab Best Buy 2014. It's the most reliable dive computer on the market, which is echoed by its five year warranty.
  • Suunto Zoop Novo Nitrox Wrist Dive Computer Suunto Zoop Novo Nitrox Wrist Dive Computer
    RRP: $400, Our Price: $349, You Save $51 (13%).
    it's a great value, easy to use, easy to see, entry level, wrist mounted dive computer for recreational divers. The Suunto Zoop Novo will not only enhance your time under water, it will also help you be a safer diver without breaking the bank.

Watch Sized

  • Suunto D4i Novo Watch Dive Computer with USB Cable Suunto D4i Novo Watch Dive Computer with USB Cable
    RRP: $800, Our Price: $719, You Save $81 (10%).
    This elegant watch style dive computer supports Air, Nitrox, Freediving and Gauge modes. With optional Air Integration, an easy-to-use 4 button interface, 9 colours, and a User Changeable Battery, what's not to like about the Suunto D4i Novo.
  • Garmin Descent Mk1 Watch Dive Computer Garmin Descent Mk1 Watch Dive Computer
    RRP: $1,399, Our Price: $1,289, You Save $110 (8%).
    This watch style dive computer has GPS, and the mapping/navigating capability is cool and handy (man-overboard locator!). It has a heart rate monitor, and tracks everything from running and swimming to playing golf and skydiving. More to the point, as a colour screen dive computer, the Garmin Descent is top-notch.

Advanced and Technical, Colour Screen

  • Suunto EON Core Wrist Dive Computer with USB and Tank Pod Suunto EON Core Wrist Dive Computer with USB and Tank Pod
    RRP: $1,249, Our Price: $1,099, You Save $150 (12%).
    A more experienced recreational diver, or beginner technical diver, would be better off with a mixed gas dive computer with a large colour display. The ScubaLab Testers Choice 2018 award winning Suunto EON Core is designed for serious divers, and covers Air, Nitrox, Trimix and CCR diving. We like the large, easy-to-read colour display, plus the ability to have up to ten tank pods to monitor the pressure in your own muliple cylinders, plus the cylinders of other divers.
  • Shearwater Research Perdix AI Dive Computer Shearwater Research Perdix AI Dive Computer
    RRP: $1,350, Our Price: $1,249, You Save $101 (7%).
    This full colour display dive computer is the choice of serious technical divers. It won Testers Choice for air-integrated wrist dive computers during ScubaLab's 2017 dive computer review.

Take a look at our list of Top 10 Best Dive Computers, or shop our dive computers department online.

Suunto EON Core at The Scuba Doctor Dive Shop