• Stephen J. Aynsley

How To Choose a DIVE COMPUTER

Have you ever needed to buy a new cell phone, maybe because you’re a diver and your old phone went for a swim - a common ‘oops’ in our industry, but when you go looking you are inundated with hundreds of models from multiple manufacturers all with different functions and features? Well, here we’ll look at some of the basics to consider when selecting a new dive computer or indeed, your first. We'll look at what a dive computer does, and if you need one?

TIP: Use promo code Magazine in the SAGA store and get a discount on any of our dive computers.


Dive computers allow divers to extend their time underwater beyond that which is calculated by recreational dive tables. In brief, a computer will keep you updated with live information on basics such as how deep you are, how long you’ve been on your dive and how much time you have remaining based on your current depth and nitrogen absorption levels. This set of information allows you to remain underwater longer by effectively writing a custom dive plan as the dive is unfolding, adhering to pre-loaded decompression algorithms and accepted safety considerations such as displaying safety stops and monitoring ascent rates.


Decompression theory can be a complex topic for some depending how deep you dive into it (pun intended) and modern dive computers take a lot of the stress away by doing the work for you although it is still advisable to understand what/why your computer is displaying the info that it is. Despite the fact that some training agencies no longer require tables to be taught at recreational level if a student can recognise what their computer is telling them then this is deemed enough, such is the reliability of computers nowadays.

Lets look at some functions and features of computers that you might want to consider based on the type of diving you do and what you might be planning to do as that could influence any purchasing decisions you make.


Gas programming.

Enriched air (nitrox) functionality is pretty much a given these days. Nitrox use does require specific training due to greater dive planning complexities and safety considerations and even though you might not be nitrox certified (yet!) it is always going to be a good idea to ensure you have a nitrox compatible computer so that you have the option. Standard nitrox capable computers allow you to enter values up to 40% oxygen which is the maximum consideration within recreational diving. They also track oxygen exposure and adjust your schedules accordingly - again, doing the work for you.

Gas programming extends even further when we consider trimix, meaning that helium can be entered as a value as well as oxygen. These models allow for complete customization because they are used by tec divers and those who extend their range beyond the limits of recreational diving. Any purchase considerations with computers in this range will come with more than just the purchase of the machine but also with a considered investment in training if you are not already tec or trimix certified. The best computers i’ve ever used are the ‘perdix’ and ‘teric’, both made by Shearwater but both are maybe overkill for divers who won’t benefit from their advanced technical functions if all they do is recreational diving, this does not mean you should not purchase one though because they are equally capable of tracking the same basic info as a recreational computer and they have modes you can select for them to function in an open circuit recreational mode.

Regardless of which gas considerations go in to your decision making, all versions will automatically calculate repetitive dives based on the data contained within them from your previous profiles. They often have a dive planning mode that allows you to see how deep/long you are able to dive for based on the gas(es) you are using, this is a gret feature as it helps you remain conservative and it’s easier to avoid pushing limits as you can see if you need to alter a profile to a shorter or shallower dive, or maybe you need to extend the length of a surface interval to gain more time on a repetitive dive.


Wrist or console?

Wrist mounted computers are worn on your arm just as you would with a watch. The displays can vary in size, again to use perdix and teric as examples (or Scubapro Galileo and Suunto Zoop respectively as recreational examples), the perdix (or Galileo) has a large customizable screen that is extremely easy to read even at great depth and with limited light or visibility. The teric (or Zoop) contain much of the same features on a much smaller display area so the info is more compact (although they do a fantastic job of arrangement). If your eyesight is not so great then a larger display will make it quicker and easier to read the information, or, you might want to consider a smaller display but with less info on the main screen. A good friend of mine made the point that he preferred a larger computer so he wouldn’t be tempted to wear it in his day to day activities and thus risking unecessary wear and tear! Console mounted computers are often part of a combo which are housed in unison with a submersible pressure gauge (and sometimes a compass) to display your remaining gas supply. The console is attached to your regulator using a high pressure hose. Alternately, consoles might be air integrated computers which eliminate the need for an SPG housed alongside it, but does require a transmitter to be used in the first stage so it can read your remaining cylinder pressure and electronically transmit that info to display on the computer - more about this later. The choice between wrist or console is based largly on preference, whilst some models are available in both configurations most aren’t. You’ll probably find a greater variety of models in the wrist mounted design as they tend to be the preference of most divers, they do have an added advantage that they are easier to travel with, especially if you still rent your regs when you go diving. Whichever confguration you choose, be sure you are comfortable accessing the required settings, it is after all giving you very important information.


Air integration

As mentioned in the previous section, air integrated computers provide additional dive data by supplying you with your remaining cylinder pressure. This is displayed digitally alongside other dive info and has the benefit of streamlining your gauges by effectively eliminating the need for an SPG. So, if you opt to dive with a wrist mounted computer then you might not have a console at all routed down your left side (traditionally speaking) as the high pressure port will now be occupied with the transmitter which reads the cylinder pressure and transmits it to the computer. This does not mean you must dive without a console, on the contrary, many divers who use air integration still like to have an SPG gauge to serve as a back up.

An extra consideration here is that despite this being a great piece of technology, they can be known at times to be erratic and maybe not sync when you are making your gear checks. I’ve had to switch out transmitters and replace them with SPG’s on some occasions when i’ve guided divers in the past, allbeit rarely - but this lends further credence to a previous point that it’s still wise to have an SPG as part of your regulator set up even if you are using a transmitter.


Alarm functions

Visual and/or audible alarms are also very common features included on most modern computers. Their purpose is to warn you when you are approaching or reach a limit, limits such as no stop time, ascent rate, max depth etc. The indicator is usually a beeping sound eminating from the computer and sometimes (depending on models) a rythmic flashing of the limit being approached. My current recreational computer is a Scubapro Meridian (updated version is the Mantis) and this allows me to personalise some alarms, for instance; I set a max. depth alarm at 28 meters to warn me when i’m approaching 30 meters, I have the safety stop set to appear automatically when I reach 5 meters to remind me to always complete the 3 minutes and I have alarms set to indicate every 15 minutes of time underwater so I can pace my dive tour. With air integrated systems you can also set tank pressure alarms so your computer will tell you when you approach your gas reserve. Again, the purpose is not to set alarms and blindly follow the computer because malfunctions can occur and batteries inevitably run dry, but more to serve as indicators to keep you aware of your place within the dive.


Batteries

Most dive computers are made with user changeable batteries. There are however a few that can require an authorised technician to perform this and it can be an inconvenience especially if you are diving or living in more remote areas, I speak from experience of my current computer which has always required a certified scubapro technician to replace it to maintain my warranty. Moving forward I woud make specific efforts to ensure any computer I have will allow me to change the battery myself although I would always prefer a dive centre to do this for me because with battery changes you often have pressure tests performed too which tests and maintains the integrity of the seals surrounding the battery chamber.

Let’s wrap things up with some quick points…

Computers can also include extra features such as digital compasses - which you should keep calibrated for accuracy, customisable straps - Suunto offer various metal or rubber strap options which are changable, colour variety - Aqualung i200c is a perfect example of having a range to colour coordinate.


To go back to the top and answer the question; “do you really need a dive computer?”, unless you understand dive planning using the tables and are prepared to dive the profiles you plan then yes, you do need one if you wish to get more out of your dives. Divemasters do incredible jobs of supervising and guiding but should not be relied upon as a substitute for your personal plan, each diver is responsible for making their own agreed upon plan and sticking to it.


….and finally - read the user manual! Be familiar with the basic functions and this will reduce a lot of new user stress. theres nothing worse than having a new computer and not knowing what it is telling you or not knowing how to navigate any categories or find the nitrox setting. You don’t need to know every feature of the computer, there will be settings you’ll never use and that’s fine, but there are some features you should understand and this is made easier if you read the manual! TIP: Use promo code Magazine in the SAGA store and get a discount on any of our dive computers. Our contributor Stephen J. Aynsley is a 4-year PADI Platinum Awarded Course Director in Utila, Honduras. Follow him on Instagram @padicoursedirectorsja or on Facebook

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