Basically, dive computer is a device that shows you depth, Elapsed Dive Time, temperature, No-Decompression Dive Time Remaining and many other things, depending on the model you use, dive mode, and whether you are underwater or on surface.
But the main task of the dive computer- is to calculate the nitrogen loading and oxygen toxicity levels and compute the most optimal and the safest surfacing procedure, manage decompression, and the surface interval between the dives. In shorter words - it helps us staying out from getting into the Decompression Sickness as long as we obey safety rules, warnings and alarms.
It simplifies our diving by replacing Recreational Dive Planners (RDP) and Wheels (but it is still a good idea to keep RDP or Wheel as a backup)!
All models are manufactured in the following mounting options:
  • computer consoles (Aeris Atmos ai, Mares Puck Air, Suunto Cobra);
  • wrist dive computers (Oceanic OC1, Cressi Archimede 2, Tusa IQ-950 Zen Air);
  • wrist units (Mares Icon HD, Uwatec Galileo Sol, Tusa IQ-850 Sapience);
  • scuba masks (Aeris CompuMask, Oceanic DataMask
Depending on the computer, you may have following dive modes:
  • Air;
  • Nitrox;
  • Gauge;
  • FREEdive
Some of the scuba dive computers may be programmed for up to 3 gas mixes and with possibility of switching between them during a single dive, and computer HelO2 by Suunto, may be programmed for up to 8 gas mixes, and can be used for diving with Air, Nitrox, and Trimix.
Next feature is the air-integration. You will meet three options here:
  • hose air-integrated dive computer;
  • hoseless air-integrated dive computer;
  • dive computer without air integration
With hoseless (wireless) air integration you need to have a transmitter installed on the regulator. Many of hoseless air-integrated models have Buddy Pressure Check feature, which means that you may check air pressure of your 'buddy' using your own computer if your buddy's transmitter is correctly paired with your computer.
Another important feature is compensation for Altitude diving. Many units these days automatically compensate for altitude diving and give you adjusted no-decompression times and depths, according to your current altitude. In some models you may set up manually altitude in certain ranges, like in Suunto and Mares brands.
It is worth to mention here Personal Conservative Factor adjustment. Just as an example - if Aeris computers allow us to set this factor just to ON/OFF state, Mares and Suunto models give us possibility to increase or decrease level of conservatism by choosing between highest and lowest levels. And this gives us possibility to set our computer for either liberal or conservative diving.