A dive computer allows divers to extend their time and safety while in the water. After your mask and snorkel, your dive computer should be one of the first things you 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 using dive tables. The dive computer changed this significantly by being able to calculate your max dive time based on the actual dive allowing multilevel 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.
But lets start with the most basic of questions - How do Dive Computers Work?
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 using dive tables. The dive computer changed this significantly by being able to calculate your max dive time based on the actual dive allowing multilevel 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.
But lets start with the most basic of questions - How do Dive Computers Work?
How Do 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. 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. 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.
Algorithms
At the heart of every dive computer is an algorithm and there are various different algorithms in use across the various manufacturers
The algorithms work out your Nitrogen loading based on your dive profile but they won't give the same results as one will be more conservative than others. 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.
The best known Algorithms are:-
The algorithms work out your Nitrogen loading based on your dive profile but they won't give the same results as one will be more conservative than others. 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.
The best known Algorithms are:-
Haldane / Spencer Algorithm
The PADI tables that were developed by Rogers and Powell are based on this model as well as being used by Oceanic and Sherwood in their diving computers.
Modified Haldanian Algorithm
This was a model that was originally used by Mares and some updates to the original Haldane/Spencer Algorithm.
Reduced Gradient Bubble Mode (RGBM) Algorithm
The RGB Model is based in part on Wienke and Hamilton’s research and work. The first dive computer manufacturer to incorporate this model was Suunto. In the meantime it’s used by nearly every manufacturer. This model considers micro bubbles in the blood stream coming from the nitrogen build-up. The thought behind it is that these micro bubbles are the starting point of larger bubbles which then lead to DCS (decompression sickness).
The Suunto RGBM Heritage
At the heart of every Suunto dive computer is the reduced gradient bubble model (RGBM) algorithm – that calculates decompression for a dive. Relentlessly pursuing ever better models for divers of all types, Suunto continues to push for RGBM perfection. Suunto has been developing RGBM algorithms together with Dr. Bruce Wienke for well over a decade. A rich history full of science, development, and underwater experience lies within every Suunto dive computer.
Suunto RGBM
The Suunto RGBM pioneering algorithm for managing dissolved and free gas in blood and tissue, this adaptable algorithm provides an accurate picture of what’s happening in the body throughout a dive.
Suunto Technical RGBM
An advanced algorithm that provides flexibility and safety during ascent through continuous decompression. Created especially to meet the needs of technical divers, it eliminates the need to constantly monitor depth, time, and when to switch gases, and means all critical data can be provided through a single device.
Suunto Fused™ RGBM
The new Suunto Fused™ RGBM algorithm seamlessly combines the benefits of the Suunto Technical RGBM with the latest full RGBM for deep dives. It has rebreather capability and supports dives down to 150 m.
With no input from the diver, Suunto Fused RGBM automatically switches between the two models to effectively manage the risks of decompression sickness.
DR. Bruce Wienke:
“RGBM is the most realistic model in science. The parameters are correlated with real data of thousands of dives which makes it good physics, and the data is validated and correlated. I have been working with Suunto since the 90’s and Suunto’s progression from Suunto RGBM to Technical RGBM and now to Suunto Fused™ RGBM is a very natural one. The new algorithm is a supermodel that covers all types of diving.”
Suunto RGBM
The Suunto RGBM pioneering algorithm for managing dissolved and free gas in blood and tissue, this adaptable algorithm provides an accurate picture of what’s happening in the body throughout a dive.
- First on the market to implement leading scientific research in decompression modeling.
- Reliability proven by millions of successful dives.
- A pioneering effort reflected in many other dive computers on the market.
Suunto Technical RGBM
An advanced algorithm that provides flexibility and safety during ascent through continuous decompression. Created especially to meet the needs of technical divers, it eliminates the need to constantly monitor depth, time, and when to switch gases, and means all critical data can be provided through a single device.
- Founded on the proven Suunto RGBM.
- Developed together with Dr. Bruce Wienke.
- First to include helium in breathing mixes and supports dives down to 120 m.
- Thoroughly tested with over 700 field dives by Suunto test diving team and validated by comprehensive laboratory test dives.
Suunto Fused™ RGBM
The new Suunto Fused™ RGBM algorithm seamlessly combines the benefits of the Suunto Technical RGBM with the latest full RGBM for deep dives. It has rebreather capability and supports dives down to 150 m.
With no input from the diver, Suunto Fused RGBM automatically switches between the two models to effectively manage the risks of decompression sickness.
- Helps maximize bottom time while minimizing ascent time; novice divers can use the same Suunto dive computer including Suunto Fused RGBM as they advance in their hobby.
- Provides a slow continuous ascent from depth so technical and deep divers have shorter total decompression time.
- Thoroughly tested with over 1,000 field dives by Suunto test diving team and validated by comprehensive laboratory test dives.
DR. Bruce Wienke:
“RGBM is the most realistic model in science. The parameters are correlated with real data of thousands of dives which makes it good physics, and the data is validated and correlated. I have been working with Suunto since the 90’s and Suunto’s progression from Suunto RGBM to Technical RGBM and now to Suunto Fused™ RGBM is a very natural one. The new algorithm is a supermodel that covers all types of diving.”
Pelagic
Some manufacturers such as Oceanic have understood the issue of multiple algorithms being used so they have coded dual algorithms into their dive computers, so you can dive on their Pelagic DSAT algorithm (Haldane/Spencer), similar to the ones you have been taught, such as the PADI Dive tables or for a more liberal dive with longer NDLs. Or you can set your computer to a Pelagic Z+ algorithm to match your buddy's dive computer so you can match their profile better.
The Pelagic DSAT is designed for your warm water, minimal effort diving so it allows you to stay down longer whereas Z+ is more for the rigorous demands of repetitive, cold-water decompression diving at altitude.
The Pelagic DSAT is designed for your warm water, minimal effort diving so it allows you to stay down longer whereas Z+ is more for the rigorous demands of repetitive, cold-water decompression diving at altitude.
What functions are important to you?
So now you know how they work, you have to decide what functions are important to YOU.
Wrist-mount or Console? Air Integration? Multiple Gases? Colour Screen?
As today's computers offer you lots of options, configurations and features, start by identifying which designs and features best fit your diving style.
Air and Enriched Air (Nitrox)
Pretty much all 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. 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.
Remember you need to be trained to use Enriched Air (Nitrox) or Trimix
Remember you need to be trained to use Enriched Air (Nitrox) or Trimix
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 whilst with others you have to purchase them separately.
Wrist or Console Mounted
Decide where you want the information displayed.
The fashion in the UK is for wrist mounted computers whereas in other areas console mounted computers are the norm. 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 computers are larger and are attached to your equipment via a hose. This makes them less likely to be mislaid. Console mounted computers use battery power even if only training in the pool meaning the more you practice, the more you will spend on batteries. 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 cylinder in order to show a pressure reading, but this does not mean that the computer is connected to the air source too. Wrist mounted computers can be used for other purposes such as free diving.
The fashion in the UK is for wrist mounted computers whereas in other areas console mounted computers are the norm. 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 computers are larger and are attached to your equipment via a hose. This makes them less likely to be mislaid. Console mounted computers use battery power even if only training in the pool meaning the more you practice, the more you will spend on batteries. 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 cylinder in order to show a pressure reading, but this does not mean that the computer is connected to the air source too. Wrist mounted computers can be used for other purposes such as free diving.
How Good are your eyes?
While the newest screen displays have improved the readability of computers, for some divers, bigger is still better meaning you will be better with a wrist based 'brick' than a watch style computer.
Multicolored displays can help highlight info.
Multicolored displays can help highlight info.
Air Integration
With an air integrated dive computer you have another great benefit in that the computer can also calculate your breathing rate, telling you how much time you have left to dive at your current air consumption. 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).
Alarms
Which options do you want for personalising your settings? Your choices used to be limited to meters versus feet. Now your options include adjustable safety factors and a choice of audio and visual alarms, deep stops, and depth warnings.
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 back light 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 cylinder pressure alarm on integrated computers is useful so your computer will tell you when you get low on gas. And NDL alarms tell you when you get close to your no decompression limit.
Which options do you want for personalising your settings? Your choices used to be limited to meters versus feet. Now your options include adjustable safety factors and a choice of audio and visual alarms, deep stops, and depth warnings.
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 back light 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 cylinder pressure alarm on integrated computers is useful so your computer will tell you when you get low on gas. And NDL alarms tell you when you get close to your no decompression limit.
Colour
Some computers come in an assortment of colours - you are on your own on this one as there is no accounting for taste!
User Changeable Batteries
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 this is more expensive than doing it yourself, having a recognised service centre such as us here at Dive Rutland complete means it is much less expensive than a new dive computer (if you get it wrong) and here at Dive Rutland on watch style computers when we change batteries as part of the service a full water pressure test is also completed
Usage
At the end of the day, the computer is only as good as you use and interpret it. It does not know whether you worked out a few hours before diving and are somewhat dehydrated. It does not know whether you got enough sleep or not. Until then you have to assess yourself before diving.
And please do not try to trick your dive computer by using more than one at a time. Some divers decide to use more than one dive computer so that on their second dive the new dive computer has no memory of the first dive and thus does not provide the appropriate warnings for a safe dive. It’s plain stupid to do this. Dive computers are designed to keep you safe so do your part and let them do their job!
And please do not try to trick your dive computer by using more than one at a time. Some divers decide to use more than one dive computer so that on their second dive the new dive computer has no memory of the first dive and thus does not provide the appropriate warnings for a safe dive. It’s plain stupid to do this. Dive computers are designed to keep you safe so do your part and let them do their job!
Conclusion
Remember purchasing a computer is going to be one of the most important purchases you are going to make so, use your local Dive Centre for advise and purchase, as we say buy from the internet you get internet prices and internet service, meaning you are reliant on the manufacturers instructions (which you should read anyway regardless to where you purchase from!).
If you purchase your computer from us, here at Dive Rutland, we will take you through the setup and best practise usage for you based on your current level of training. Handle warranty issues for you and in the future when you have questions, we will continue to support you.
If you purchase your computer from us, here at Dive Rutland, we will take you through the setup and best practise usage for you based on your current level of training. Handle warranty issues for you and in the future when you have questions, we will continue to support you.
What Do you have in Stock?
We hold a range of computers in stock - not able to come in just yet have a browse of our online store which shows a subset of our stock
v1.02 25th June 2020/V1.00 Club Newsletter March 2018