No longer common as trends and technology have moved on and the cost of mixed gas computers has come down.
These are the standard computers in use today by many recreational divers. They allow the diver to use Air or Enriched Air Nitrox of mixes up to 40%.
Many have a gauge mode and a dive mode. Some have a free dive mode
These are normally not decompression computers and work within the Non Decompression Limit’s.
These computers allow the diver to use Air and Enriched Air Nitrox, some up to 100% Oxygen content. Some are able to use Helium in the gases.
They also allow the diver to switch between gases during the dive.
These normally have a decompression mode.
Shearwater have Gauge / OC (Open Circuit) Recreational / Tech / CC (Closed Circuit) Tech.
Buhlmann Gradient factors vs RGBM (Reduced Gradient Bubble Model aka Bend and Mend)
Watch this extremely interesting talk by Professor Simon Mitchell and you make the decision on which algorithm you prefer.
Doing a big dive, or perhaps it’s cold or you are not as fit as you used to be? Well most computers allow you to increase the safety aspect through conservatism or gradient factor settings.
Small watch sized screen or larger easier to read.
Backlight mono screens, hard to see in low light, press and hold a button to the light up the screen for 10 to 30 seconds.
High Resolution vivid enhanced colour display screens that are always clear and easy to see even on the darkest dives.
Inbuilt digital compass
Read the gas in your tanks. Some work out your breathing rate.
Single tank or multiple tanks transmitters options
A computer on the wrist is the easiest option. It’s easy to see and you don’t have to hold it, so great for when you are using your hands for a task.
Gauge mounted are great if you don’t want to risk losing your computer. The down side is you have to pick it up every time you want to read it and when you are making a descent or an ascent, you have to hold it to watch your depth or ascent rate.
Some cray hunters do not like wrist mounted for risk of scratching the screen. My personal view is that with a little bit of thought and good buoyancy, it isn’t an issue. Put the computer on the wrist of the hand you are not using, or turn the computer so the face is away from the rock.
With the computer still on your wrist, especially a back lit one with air integration, you can be safe knowing you are not getting close to your NDL, max depth or low on air whilst in darker tighter spots.
Heads up displays have been on the market for the rebreather divers for a while from Shearwater. Now they are developing one for the rest of us. It is the Shearwater Perdix AI, but in a much smaller case that fit to your regulator hose. So you do not have to move to see your computer, you simply move your eyes slightly and refocus.
Some computers by Suunto and Scubapro/Uwatec need to go back to the authorised service station to have the battery changed. This is timely and quite costly, well over $130. But there is the assurance that it is done under warranty and is tested in a pressure pot.
Some computers take button batteries that you can change yourself. There tends be a special tool to undo them and some small parts involved. An outer case locking mechanism, a watertight door, a positioning bar and an O-Ring. The batteries are pretty cheap, normally under $15, but not as common in some areas, so be sure to have spares. If the computer is small enough, we can do that here and then pop it into our testing pot.
Shearwater Perdix AI uses a $1 AA battery that you change a little more regularly, but it is just a matter of unscrewing the double O ring door with the tool they provide or a coin. These batteries are commonly available worldwide.
Rechargeable computers such as Suunto EON Steel and Core make batteries a thing of the past. However you need access to a power supply. The battery life of a full charge is not clear as they state between 10 to 20 hours. The computer will not allow you to dive if it has less than 2 hours of battery remaining.
Shearwater Perdix AI and Suunto EON Core allow you to customise the information displayed to suit your needs. You can also change the language from English.
Most computers can be connected to a PC or even a phone to download your dive logs. There are some software updates that can be done from home too.
Be aware that some computers will lose your dive logs when changing a battery or getting software updates. So don’t be disappointed, download your dives regularly.
One of the most important things to remember is to learn your computer before you dive it and be sure it is in the correct mode before jumping in. As soon as they are wet, some will not allow you to change modes for up to 48 hours after the water contacts dry.
Some Nitrox able computers return to 21% when it comes out of dive mode. So be sure you are at the correct O2% before jumping in.
Make sure you are in the correct mode before jumping in. I have seen someone accidently dive in altitude mode and so they had very little bottom time.