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Dive Computers: What are they and why you want one

An blog post for all you scuba divers or aspiring scuba divers out there. If you’ve been to a dive site before, you’ve surely seen them. Typically what looks like an oversized watch on a diver’s wrist, on their instrument console or even hanging by a lanyard, dive computers are everywhere. A dive computer simplifies a diver’s life in a lot of different ways. I’m going to talk about what dive computers are, what they do, their advantages and why you want one.

What are Dive Computers and what do they do?

Dive computers are electronic devices that, at a minimum, act as:

1) A dive timer;

2) Digital depth gauge;

3) A computer to calculate your real-time No Decompression Limit (NDP); and

4) Memory/Logbook – keeps a history of the dive (bottom time, depth, temperature)

By using your current depth (depth gauge) against the time you spent at that depth (dive timer) a dive computer can calculate how much nitrogen you have accumulated in your tissues over time. The rate at which we absorb nitrogen from our air supply is directly related to our depth. In diving this is very important as an excess of nitrogen in your body can lead to Decompression Sickness (DCS), which is a problem that can lead to serious injury or death. Lucky, we can avoid DCS by simply limiting our nitrogen absorption. A dive computer, based on all your diving you’ve done during the day, will tell you in real-time how much time you can continue to stay underwater without risking getting DCS.

** Of course, your remaining time is based off of theoretical models and it is still possible to get DCS even while staying within the computer’s limits. Personal judgement should always prevail. However, the safety record of the theoretical models is extremely good. **

Some additional features available on some dive computers:

1) Nitrox compatible – The ability to use air mixtures > 21% Oxygen with their corresponding calculation changes

2) Air integration - Functions as a air supply pressure gauge and can calculate how long, in minutes, the diver’s air supply will last. This can be either through the computer being directly connected to the diver’s tank or can be wireless through the use of a transmitter.

3) Digital compass

4) Computer downloadable – Logbook can be downloaded to a computer


Key Advantage: Longer allowable bottom times – Due to real-time nitrogen accumulation monitoring/calculating

The biggest advantage of a dive computer is that you don’t have to mess with dive tables anymore. Dive tables are a paper copy, simplified version of your nitrogen accumulation while diving. While using dive tables is a valid and safe way to dive, they must be used before the dive starts only accounts for the maximum depth of the dive. Essentially, a dive table assumes a dive that starts at sea level, drops immediately to maximum depth, then ascends immediately to the surface. This is not the case during most dives as the diver will be constantly changing depths to explore different areas of the dive site. In all cases, a dive computer will allow for more time underwater (longer NDL) than tables because it accounts for nitrogen accumulation at all depths, during all the parts of the dive. (Pic above: PADI Dive Table)

Additional advantages:

1) Simplifies dive planning as computers are easier to use than dive tables (both air and Nitrox)

2) Can reduce the amount of gear the diver carries – depth gauge and timer in one package. Additional pieces of gear can be eliminated depending on which additional features are included (compass, pressure gauge, etc). However, this is at the compromise of redundancy.

3) Automatic dive logging with the possibility for computer download (if available)

Why You Want One

There are absolutely no disadvantages to using a dive computer. It makes knowing your NDL fast, easy and convenient. You can dive safely and for longer than using dive tables. Additional features that can be found on dive computers can make your dive even easier (ie. air integration), can eliminate other pieces of essential gear (ie. compass) and makes logging easier post-dive. I highly recommend a dive computer for your next and future dives!

Dive Computers I’ve used (with their additional features):

Here’s all the dive computers I’ve used personally. They all have the basic features in a dive computer that will keep you diving safely. The differences in price will get you some of the additional features which are “nice to haves” if you can afford them.

Suunto Gekko/Zoop – Nitrox, Computer downloadable (cable required, not included) – $249.95

Oceanic Veo 180 – Nitrox, Computer downloadable (cable required, not included) – $199.95

Oceanic Atom 3.0 – Nitrox, Wireless Air Integration, Computer downloadable – $999.95

Oceanic VT 4.1 – Nitrox, Wireless Air Integration, Computer downloadable, Digital Compass – $1099.95

- Chris

PADI Open Water Scuba Instructor

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