Dive computers are wonderful inventions and have made diving a safer and more enjoyable sport. No diver has ever said “I miss having to work out my dive plan using dive tables’ at least not someone diving within the no decompression limits anyway.
What a diving computer does is take samples of depth and time from your dive and from that information it calculates your no decompression limits or your decompression requirements. So as a diver we can see at a glance in big fat digits, how much longer we can spend at a giving depth and what safety or mandatory stops we should do before we surface.
The introduction of computers has all but eliminated the need for recreational divers to pre-plan each dive using dive tables to ascertain the maximum depth and time allowed for each dive. The diver relying on dive tables would need to monitor the depth on a depth gauge and carry a diving watch to monitor the elapsed dive time to ensure they didn’t exceed the allowed maximums of their plan.
Computers have made diving safer by removing the element of human error calculating no decompression limits and they’ve made diving a lot simpler and more spontaneous.
The greatest benefit dive computers have given us is they allow us more time in the water. The do this by sampling our depth every few seconds and by giving us credit for time we spend at shallower depths whereas dive tables assume the entire time is spent at our maximum depth.
Dive Computer Features
The most basic task of your dive computer is to display essential information about your dive in real time. You want to be able to see your depth and time as well as your no stop limit and no stop time remaining. No Stop time refers to the amount of time you can spend at a certain depth while still being able to make a direct ascent to the surface should you need to.
You will notice your computer update as you change your depth. As you go deeper you will have less ‘no stop’ time remaining and as you ascend to shallower depths your no stop time will increase.
Other important information you should expect from a computer is your ascent rate with a warning indicator to alert you to when you are ascending too fast. Depending on the computer’s algorithm the ascent rate will be set somewhere between 9m and 20m per minute. Your computer should also display and alert you to a decompression obligation should you exceed your no stop time limits.
Most computers will have a lock out mode which shuts you out of the computer for a given period if you violate the decompression obligation it has set out for you. This is your queue to sit out the next dive and not dive again until the computer has regained function.
Other import features that you should consider standard are indicators for a low battery in the computer and it should also have the ability to access a history of past dives.
Wearing Your Dive computer
Dive computers can be configured as part of you scuba unit by being included in a console with your pressure gauge on the end of your regulator high pressure hose. This set of gauges can also include a compass. The other most common way to wear your computer is around your wrist like a watch.
Many of the current dive computers are made as a puck which is independent of the rubber gauge boot or wrist strap it comes with. This means that if you at some point change your mind about how you wear it, you can pop out the puck and reconfigure it in the housing you wish.
The choice of wearing your computer on your wrist or within a gauge console is a personal one and each with their own pros and cons. If you have a wrist mounted computer you may be more inclined to forget to take it with you when you go diving which is much harder to do when the computer forms a part of your regulator set. If your computer is attached to your reg set you will have to pay extra attention to how you clip it off to your BC to avoid dragging it over the reef or ocean floor.
Dive Computer Optional Extras
On top of the standard features you should expect from all dive computers there are a number of additional features that you may want to take into consideration when you’re deciding on what dive computer to buy.
Air integrated dive computers can replace the need for a SPG (pressure gauge) to monitor the remaining air in your tank. These computers track the remaining pressure in your cylinder and can warn you with alarms and alerts when you are getting low on air.
You can have an air integrated computer on the end of your high pressure hose or wear it on your wrist. Wrist worn units require a transmitter to be attached to a high pressure outlet of your first stage regulator to transmit your tank pressure from the tank to the computer. The thing to keep in mind with computer transmitters it they require a battery to run which adds one more point of maintenance to your scuba gear.
TIP: If you use an air integrated wrist computer with a transmitter on your first stage, the transmitter itself can be vulnerable to being hit on objects during a dive or it can be damaged if someone careless picks up your gear by the regulator first stage. It’s a good idea to put the transmitter on a short (3 inch) high pressure hose which will act as a shock absorber for it if one of these situations arise.
Mixed Gas Capable
If you dive with mixed gases or you plan to in the future you should take that into consideration when looking to purchase your own computer.
Using a computer to dive on Nitrox or enrich air is the same as using to dive on air only, the difference being in setting your computer up pre-dive for the percentage of oxygen you will be breathing in your gas mixture. While Nitrox capabilities have become somewhat standard in dive computers there will be a difference in what concentrations of oxygen they will accept and if they only allow one Nitrox mix or if they will let you switch mixes during a dive, if for example you’re carrying a different decompression gas.
There are also Trimix computers available to take into account any helium that might be in your breathing mixture. It is important to note that diving with multiple gases and outside of decompression limits requires extensive training and pre-dive planning. You should never conduct these types of dives relying only on information from your dive computer.
Many computers will allow you to download your dive data to your PC after a dive. This can be a great way to keep a log book as the information is very accurate and will include your dive profile. They will also let you view times during the dive where you have acceded normal ascent rates.
User Replaceable Batteries
Replacing your own computer batteries can be a plus or minus depending on how careful you are doing it. On one hand, changing the battery yourself can save you the trouble of sending your computer away or leaving it with a dealer while they change the battery for you. Particularly if your the type of person that checks you gear right before taking off on a trip. There’s nothing worse than discovering a flat battery and not having time to replace it.
Care must be taken when changing batteries yourself and it should be done in a clean dry area. Any sand or dirt getting on the o-ring or battery compartment can make your computer non-waterproof very easily.
Choosing a Dive Computer
Like with the choice of any gear, choosing a dive computer should be first based on the type of diving that you do to ensure that it has the features and functions you will need.
If you dive in cooler water and wear thick gloves you will want to avoid a small computer with small buttons that are positioned closely together, where as if you struggle with poor eyesight you will want a computer with a large display and may even then mount it on your wrist so that you can raise it closer to your face.
If you travel a lot with your diving you may want a computer that doubles as a wrist watch to allow you to lessen the amount of gear you travel with.
There is also a lot of personal preferences that go into choosing a computer. If you are the sort of person that likes their gadgets you will probably get more enjoyment out of a computer that has all the bells and whistles. Or, if you are not a very technically minded person and just want the basic dive information, a more simple computer that displays everything on the default screen is all that you will need.
And of course, price plays an important role in choosing the right dive computer for you. Of all the SCUBA gear we accumulate, the computer probably has the largest range in terms of price. A cheaper computer may lack some features that you want. On the other hand if you are on a limited budget, over spending on a computer that has functions you don’t need may prevent you from spending money on other pieces of equipment that will serve you better, such as an appropriate dive suit for your conditions.