Are you in the market for buying a dive computer? In this article, we explain what you should consider before you make your final purchase.
Using a dive table, divers are given an NDL for the maximum depth of the dive, if they are planning a multi-level dive, it is more of the same, how long at each level. While they will try, most divers do not dive like that.
A dive computer uses the same principals as the dive tables but are using actual conditions to give you your NDL in real time. It can help a diver avoid decompression sickness while giving them the maximum safe bottom time for their dive profile.
Dive Computer 101
The science behind the recreational dive tables is very complex and took decades to refine to their current state after centuries of study. The human body has many different types of tissues, plus bone, blood and brain matter.
Each of these absorbs and releases nitrogen at different rates. These are grouped in half-lives, the time it takes for half of the nitrogen to leave the body. These half life's range from 2 minutes to 6 hours, with an overall average of 60 minutes.
Recreational dive tables are set on the concept of a diver slowly and steadily ascending from their maximum depth to the surface. As they do, nitrogen will leave the body at their half life rate. The NDL time shown on a table represents the longest time that a diver can stay before they reach a point where the body can not return to a safe level before reaching the surface.
Dive computers use the term tissue or compartment to represent one of these groups. The average computer uses 9 to 12 tissue groups in their calculations while one computer uses eight tissue compartments.
The dive computers have taken the mathematics behind the dive tables to create formulas that the computer uses to determine the level of nitrogen in the diver at any given time. These formulas called Algorithms are using depth and time measurements and applies them to each of the selected tissues. The result of the group with the most influence on your decompression is shown on the dive computer.
While there are possibly a hundred different models of dive computers produced by over a dozen manufacturers, there are only seven different Algorithms in use.
A few use a combination of 2 models know as the Haldanean model combined with RGBM (Reduced Gradient Bubble Model).
While they do show differences in NDL, they provide very similar results. When getting into decompression dives the result varies more. Some computers are more conservative then others, and some models let you add an extra level of safety if you wish. Most models have the ability to perform Nitrox dives up to 40% while others extend their functions to include multiple gasses of tech diving and other features. Besides the basic functions manufactures have added different features to target different users.
Air integration computers will show the amount of air you have remaining in your tanks. However, many are also able to use your actual usage to refine the calculations of nitrogen you are absorbing.
These may be connected to your high-pressure port, or you can receive the information by a transmitter connected to the tank.
Most dive computers now have the option for the battery to be replaced by the user. Older models might require that the battery is replaced by a technician and is pressure tested.
If you have an older model, you should consider servicing your dive computer before you leave for your next scuba trip to ensure that it will be fully charged and able to function properly for the duration of your diving adventure.
Planning a scuba trip? Yes? Then you should download the ultimate scuba dive checklist today so you will not forget to bring anything you need.
Console or Wrist Versions
When it comes to dive computers, you can choose from a few different models. Some models come in both wrist and console versions while some are in just one mount. Wrist versions can be the traditional larger model or one that is a watch.
Memory and Downloading Abilities
Being able to download your dive information from the dive computer to a personal computer gives you the ability to look at every detail of the dive at any given time in the dive. Some computers now use WIFI and can transmit directly to a cloud server for storage.
Nitrox/ Air or Trimix
Most recreational computers are also used for diving nitrox up to 40%. Trimix used by technical divers are available on some dive computers.
Free divers love using dive computers with heart rate monitors built in. For divers at different levels, there are features that focus on their needs.
What other scuba divers say (via Facebook) regarding buying a new dive computer:
Chris Lang says: It should be ease of use, and you should be able to read the display easily at all times.
Darren Rawlings says Get something that's suits your diving, so it's either no frills or all the bells and whistles!
Sean Allison says:
I'm a Divemaster, and I teach our computer lecture during open water classes. I tell students that the computer should fit their needs, but some standard basics should be: audible alarms, settable alarms, ease of use, Nitrox compatibility (if Nitrox certified), backlighting, and countdown timers for deep stops/safety stops.
John Tackman says:
It should be reliable and readable, avoid unnecessary bells and whistles ( no point getting a top-of-the-line trimix deco computer if you're only diving rec air )
Be a smart diver and keep using common sense and do not let a dive computer interfere with that. Using a dive computer allows you to make more complex (deep dives) with less planning. Remember always to dive within your limits and do not make dives you are not trained to do. Rely on proper planning and common sense backed up by a dive computer.
What are your considerations when buying a dive computer? Share your thoughts with us in the comments below
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Blog written by: Rutger Thole who is an avid scuba diver and loves to travel, dive and write about scuba diving.