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Things to Consider When Buying A Dive Computer
When you look at a scuba diver with all their hoses and black neoprene it is easy to bypass one of the most important pieces of equipment. The Dive Computer. This small watch like accessory is so much more than is seems.
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What Is A Dive Computer?
When recreational scuba first came into being in the 1940s divers used a special set of tables to plan dives. Coupled with a depth gauge and timing device, these tables helped divers to stay within their no decompression limits (NDLs).
NDL is the time you can spend at a certain depth and still be able to ascend directly to the surface in a controlled manner. Breaching these limits means you need to make controlled stops to let off the extra nitrogen you body has absorbed.
If you breach limits and ascend straight away you run the risk of getting decompression sickness.
Some divers breach these limits on purpose however it takes special training and procedures.
The nature of the tables meant you would need to thoroughly plan your dive beforehand and end your dive when you reached the time limits for your maximum depth. That or plan a multi stop dive.
In some ways it was better as people had a greater understanding on dive limits and were more reliant on their own knowledge to keep them safe.
Dive Tables To Dive Computers
With advances in technology these decompression models were put into wrist and console mounted computers. Using special algorithms, depth sensor and timer they calculate you decompression limits in real time.
This makes them very user friendly as they require almost no knowledge to operate. They also can accurately calculate you NDLs for your personal profile. Meaning it will recalculate your NDLs on different depths.
Different dive computers use different algorithms so you may see different NDLs on a different model at the same depth. You can sometimes change these algorithms to the one you prefer using.
It is very possible to dive without a dive computer (using tables instead). Although the lower workload and need for mathematical planning before a dive make them the primary choice for divers.
They are quite pricy as far as equipment goes but at the cost of your safety it is one of the first things you should invest in.
Dive Computer Features
A dive computer can cost anywhere between 150 to 1500 dollars. The most basic ones will only have the most simple features.
Shows the depth you are at underwater.
Shows the time of day. So pretty much like a watch.
Shows you how long you have at a certain depth before needing to do decompression.
Showing when you are not allowed to fly. As flying reduced pressure even more it can lead to getting decompression sickness to soon after a dive. The same goes for mountain climbing.Â
As dive computers have to be pressure tested to make sure water doesn’t get in the low battery warning can come in handy. It allows you to plan when to hand your dive computer in for a replacement.Â
A dive computer can cost anywhere between 150 to 1500 dollars.
The most basic ones will only have the most simple features.
Ascent alarm. This usually shows as a set of bars somewhere on your computer which tell you how fast you are ascending. If you go too fast they may start beeping at you to slow down. Most models are very conservative and have an ascent rate of 9m per minute. Recommended rates are 18meters a minute. Take the warning seriously but don’t freak out if your computer starts making noise at you.
Depth alarm. Especially useful when you have depth requirements due to your training level or are using nitrox. These can usually be turned on or off depending on your preference.
NDL Alarms will tell you when you are reaching your limit.
Details of previous dives. For example time in, max depth, dive time, etc.
Accordion Content
This feature allows you to customise the percentage of oxygen in your breathing mix to correspond with the nitrox blend you’re using. You will get readjusted NDLs however you must also be careful to watch your max depth.
Consoles attach to the regulator directly. They tend to be larger and easier to read and are less likely to get lost.
Wrist mounted strap onto your arm. They can be worn day to day and used for other activities as well. For example free diving, swimming or as a depth gauge.
For most recreational divers these features are all you will need. So realistically aren’t looking at anything with a price tag over 500 dollars.
The more features you add the more the price tag tends to rise. When choosing these features consider the type of diving you are interested in and what you may want to do in the future.
Also ask to try different models if they are available whilst doing training courses to get a feel for the features you like best.
Advanced Dive Computer Features
A transmitter or hose connection will allow you to read how much air is in your tank on your dive computer screen. All your data will be in one place. You can also calculate breathing rates and therefore how long your air will last.This eliminates the need for an air gauge but it may be a good idea to keep one as a backup.
For seeing important information in low light environments.
For the hard of sight or to simply make your life a little easier. Although they do tend to take up more wrist space too.
This means you have the ability to adjust the conservatism of your computer. It is more useful for people doing technical diving or who understand how the gradients work.
I like to use the old fashioned version but a good backup in an emergency.
Is a feature that activates dive mode on entering the water. It helps save on battery but with models that double as a watch it may be better to have it active constantly.
Allows you to download dive data onto a pc or mac using software. Useful if you want to keep a digital logbook.
This is a feature used for technical diving where you will need to be switching to different gas mixtures during a dive.
To tell you the exact temperature of the water. Good for gauging exposure protection and planning your next dives.Â
Very useful as you don’t have to pay to get your battery replaced or wait out of the water while its in the shop.
Additions
Changing The Battery
In computers that are not rechargeable you will probably come to a point where the battery will need changing.
The compartment where batteries are stored are watertight. To keep them watertight there is usually a o-ring/rubber seal between the edges of the lid and compartment. The amount of pressure applied when the lid is screwed on is very important. If it is too loose then water will get in. If it is too tight the o-ring will either get damaged or change shape also allow water in.
It is possible to change your own battery if you have the correct screwdriver however it is also very risky. For this reason most people take it to a service centre. Its more expensive than the DIY option but definitely cheaper than a new dive computer. You may also void any warranty if you choose to replace the battery yourself.
Straps
Plastic straps are known to wear and break over time. Especially in places where they are constantly being readjusted. To combat this you can either replace it with a fabric strap to begin with or wait until it breaks and then replace it with another plastic or fabric strap.
Screen Guards
Stop the screen getting scratched much like a phone. They are useful as carrying around tanks and scuba gear its very likely you will scratch the display.
Aftercare
A few rules to follow once you have bought your computer.
- READ THE MANUAL
- Don’t share your dive computer. It tracks your personal nitrogen intake. Incorrect data could put you or the person you share it with in danger.
- Stay well within your limits. A good practise is to start heading up when you get down to 5 mins on your NDL.
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Also check out our other handy equipment guides.
If you have anything you would like to add that you think could be helpful to someone buying their first computer, please drop a comment below!
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Katie Braunstein
I have been a traveler my whole life, having been born in Zimbabwe but growing up mostly in the UK. I first got into diving three years ago when I met my partner and fell in love. Since then it has been my passion to share this love of our underwater world with others.
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