Blog about Underwater Life and Scuba Diving

Dive Computers – Our Aquatic Personal Assistants

1 Star2 Stars3 Stars4 Stars5 Stars (1 votes, average: 5.00 out of 5)

Computer Vs. Tables

I tap my air gauge to indicate that I’d like to know my buddy’s air situation, he signals back that he’s still got over a hundred Bar, I look at my gauge and see that I’m also over a hundred, so I signal that we could head a little deeper to investigate the ship’s lower decks if he wanted to – they didn’t look that interesting on the dive map so we didn’t plan for them, but from down here they look very inviting – my buddy agrees with me and gives the “ok”, so we descend…


The situation described above is a fairly normal situation when diving a site you don’t know. You may have looked at maps of the site, but ultimately you won’t know where you want to go until you’re down there. The problem with this is that if you don’t know where and, more to the point, how deep you wish to go then your planning on the RDP (Recreational Dive Planner) counts for very little because it will constrict you to an inflexible dive profile that might not meet the type of dive you want to do. For the guys described in the passage above they would be diving beyond their scheduled dive plan which could cause them real problems once they surface.

The modern diver doesn’t interact much with the RDP these days. The closest most divers get to using the tables is during their open water course, or their nitrox course, and even this will come to an end soon (PADI will be phasing in the computer-only open water course in the next couple of years). And yet, for all that a novice diver will think he is not using the RDP, he will be using it every time he dives, because all dive computers use the tables for their basic model. In essence, the computer is just an electronic RDP calculator with a depth gauge, stopwatch and memory all combined into one unit. There is no ground breaking technology in it, yet it is the most researched and refined piece of gear you will find in your equipment bag.

Still Used In All Dives, The RDP Lives On In Computers Rather Than Slabs Of Plastic…

So Jamie, How Does It Work?


Em… ahem…you see…there’s a gauge right, and a…a…and it’s very complicated, you wouldn’t understand it!

Although it is very complicated (for the designers), it is also very simple (for us, the users). As the diver begins his descent the computer starts the stopwatch, this is the actual bottom time. It also begins to take readings of depth at frequent intervals (usually around twenty a second, though you can normally set it to be more or less often). For each reading it takes, it gets its tiny RDP out and does the calculation just as we do in our open water course. It then jots down the current nitrogen level in our body and also states how much more bottom time we have left at this depth. If we stay at this depth the computer will keep doing its RDP sums and count down our bottom time, if we descend further it will see that we are deeper and start doing maths to find out how much less time we have. So basically you have a little man inside your computer who is crazy fast on the ol’ RDP and he does constant and corrective calculations that give you an accurate statement of your current levels of nitrogen and how much longer you can stay at that depth…. Does that sound plausible?

You Feed The Little Man Through The Tube On The Left…

Which Computer’s Best?

Obviously everyone wants to know which model is best, to save them buying a duff product. The odd thing about dive computers is that, even though there are certainly “better” products, the actual dive computers are mostly all the same or similar. The real differences between them are how they display the information, how easy they are to use, how it looks, and what additional features the designers have managed to squeeze in. The computer’s ability to calculate remaining bottom time is generally fairly standard nowadays (with mild variations in accuracy, the mathematical model used and how conservative they are).

The answer then, is that none of the computers are better than the others, but there are plenty of reasons that you’d choose one computer over another. I’ll look into what those reasons might be throughout the rest of this article.

Take Your Pick…All Computers Ultimately Aim To Do The Same Thing!

What Does It Mean If My Computer Is Conservative?


It means your computer believes in marrying before having sex, and thinks knee length skirts are too short! Well, not really, most computers are actually very liberal and into free love and support progressive government propositions!

But in a diving sense (which is why we’re here after all), a conservative computer is one that will either give more warnings, give warnings earlier or read as though you have been deeper or have less bottom time. To put it simply, a conservative computer is a very nervous, safety conscious computer that would like to err on the safe side rather than take risks. This might sound like exactly the kind of computer you’d want, who wouldn’t like to be more safe on their dive? The answer here is that an overly conservative computer will likely drive you to insanity before you’re more than ten minutes into the dive. A twitchy computer will beep if you move your arm up too fast, it will make you do double the safety stops your fellow divers will do and you’ll end up loosing a big chunk out of your bottom time.

The key is to get a computer that has variable levels of conservatism so you can set it to a level that suits your circumstances (if you are very overweight, for instance, it might be prudent to put the computer on a more cautious setting).

Wrist Vs. Console

This is a less pressing debate now than it was ten or even five years ago because computers of today are much more compact, so there is less of an issue putting it on your wrist as it was before.  It is less a piece of gear, as a very functional piece of jewellery.

The question is, do you want the convenience of having your computer built into your regulator (usually in place of a SPG) so that you can’t forget or loose it, and you get the added benefit of having air readouts and calculations displayed on the same screen. Or, do you take the lighter, more easily read and more fashionable watch-style computer that now has the ability to take air readings too (in some cases)?

The question isn’t as pressing as it once was, but the customisation of gear is the mark of an experienced diver, and this is a personal choice that will make a tangible difference to the way you interact with your computer.

Which One? Doesn’t Matter As Much As It Once Did…


Essential Features

This is a short list of the features that most modern dive computers come with as standard, you can use this as a glossary of terms so you know what you’re looking at when staring at the back of the box in the dive store.


  • Clear Display – This is pretty much priority number one for me, if the screen is jumbled, illogical or too small then I will not be able to fully interact with the computer on a natural level. The computer must be able to plainly display all the information you need throughout the dive in a basic and concise format. Avoid busy screens, choose a large, simple display.

    As Screen Technology Gets Better, The Displays Can Show More – Colour Screens Are The Next Trend

  • Intuitive Menu System – For similar reasons as I require a logical screen setup, I need to be able to select functions, view different data and adjust settings in a coherent and rational manner. Again, simple menu systems work better for this than ten button, IQ test, Rubix Cube puzzle systems.
  • Alarms – When you’re diving you’re down there to experience the underwater world and see as much as you can, you certainly don’t want to be diving with your face attached to your computer screen. This is why alarms are useful, they will tell you if you are reaching maximum bottom time, your predefined time limit or ascending too fast. Alarms let you dive, not watch a screen underwater.
  • Backlight – Simple, you want to see your computer on night dives and in bad viz? Get a good back light that will operate for long enough to let you fully read the display.
  • Comfortable – You will be wearing this wrist-top computer for at least two hours on the day you dive, and if you’re like me you’ll leave it on between dives. Make sure you test how comfortable it is (some are really bulky and very uncomfortable).
  • Thermometer – It might seem like a frivolous feature that is only for curiosity’s sake, but a thermometer is useful for lots more than just telling your friends how cold it was on your ice dive! A thermometer can help you work out your temperature tolerance (look in the log book, see that last time you dived in twenty degrees you wore a five millimetre and you were cold, now you know to take a seven millimetre suit) or it can give you an idea of what wildlife will be around, or not.
  • Ascent Rate Indicator – One of the most used features on a computer, this monitors how fast you go up. If you go too fast it will warn you so you can slow down. This is great for letting you relax as you ascend, if the computer is reading green then you can just enjoy the last of your dive, not stress about the ascent.
  • Safety Stop – Another important feature of a computer is to alert you to mandatory and non-mandatory stops, at what depth and for how long. It will give a countdown and an ideal depth for you to rest at. There will be another alarm if you ignore the safety stop and it will send you to bed with no dinner (a computer can be a real nag!)


Desirable Features

This is a list of things that you might be interested in looking out for when choosing your next computer. Some are more useful than others, there is a fine line between throwaway gimmick and essential tool.

  • Air Integration – I briefly mentioned this earlier, essentially it allows your computer to monitor your air supply and not only display how much you have, but how much more time you have left breathing at the rate you are presently and the current depth. The accuracy of this is a little dubious and for most divers it is unnecessary because they can calculate their own air supply. If you are looking at using air integration with your wrist computer then you will need to buy a separate wireless transmitter that attaches onto your regulator first stage. These little devices can cost a fortune! The value of such an item is very subjective.

    Air Integration Can Add A Lot To Your Dive, And A Lot To Your Credit Card Bill…

  • Compass – Compasses in dive computers are both potentially useful and generally pointless. The fact that you can house a digital compass in the computer is very exciting, and as a backup it’s great. But, the format that it is displayed in is so unnatural that I always end up reverting to my Suunto and working old-school. Once they manage to get the display of the digital compass to equal that of an analogue compass then this will be an excellent feature.

    The Digital Compass Is Currently Just a Backup, Hopefully They Can Make It A Replacement…

  • Large and Useful Logbook – This isn’t so much a feature as a general requirement. All computers have a logbook but some are hard to use, hard to read and are too small. A logbook should be something you briefly look at, recall the data and put away, not spend an hour mining the information out piece by piece. It should also be big enough to store a two week dive holiday’s dives (at least forty hours worth in my opinion)
  • Gas Switching and Nitrox Support – This feature is becoming more essential as time and the dive industry progresses. It is also becoming more prevalent in the average computer, it is almost a standard feature now. Because divers now dive breathing gas blends and more than one mix of gas there is a need for the computer to work using different parameters. If this gas switching and mix entering is easy then it makes a complicated thing very simple, which is a good thing when divers are concerned.
  • Computer-to-PC Connectivity – This is another trend on the marketplace that will only become more common, not less. People are used to uploading and downloading their personal information onto the computer and internet (look at what we do with our personal digital pictures and what we write about ourselves online). This goes for dive logs too. A dive log program will display graphs of dive profiles and maps of dive destinations, and it will also allow you to post your dives online, for all the community to see!

    Plug It In And Post It To The Internet! That’s The Modern Diver’s Motto!


Final Thoughts

The dive computer has now been around for so long that it is no longer a luxury item that only wealthy and experienced divers used. Even divers on a budget can now buy high quality, feature-packed computers from well known brands – they’ve become that mainstream. This isn’t a random act of capitalism at work here, it’s a simple case of supply and demand – divers like having the freedom to adjust their dive profiles on the fly without having to worry about DCS creeping up on them. They also like having control over their data, and the computers that are coming onto the market are offering them new ways to manipulate, record and view their dive information. It’s the electronic age and diving is no exception!

Do you have a favourite dive computer? What features do you look for when choosing a new computer? Have you ever had one fail on you? Do you shun computers in favour of old fashioned tables? Please share your thoughts and experiences with us using the comment section below.

Happy (logged) Bubbles!

By Jamie Campbell

Tagged as: , ,


  • David - The Diving Blog said:

    I’m a little disturbed by the recent trend to only teaching dive computers in Open Water courses. PADI is heading that way and a few other agencies have already gone. What do you do if you’re in The Galapagos and your dive computer dies? No more diving for the rest of the trip?

    Nevertheless, they sure are handy!

  • Inon said:

    Great article, I’m happy with my Suunto D4, dive computer is a must for safety.
    When you feel safe at every part of your dive you are much more relaxed and can enjoy your dive.

  • Daniel said:

    I agree with David, and I’m a beginner diver. The tables are essential as backup, and in my experience, computers always seem to die at just the wrong time.


There are no trackbacks

Blog Roll