Choosing a Dive Computer

Scuba diving, though generally considered relaxing and easy for divers with experience, proper technique and gear, still requires a significant amount of calculation before and during each dive. Most scuba courses will introduce dive tables to help determine how long anyone should stay underwater at certain depths, as well as when to make decompression stops on the way back to the surface. Nowadays, dive computers make this process simpler by tracking depth, time, and no-decompression limit throughout the duration of your dive. Dive computers can track the amount of built-up nitrogen in your system during the dive to calculate at what depth and for how long you need to stop on the ascent. Read on to learn what they calculate, sought-after features, and how to choose a reliable dive computer.

What a Dive Computer Displays

Dive computers provide you with the same information gleaned from dive tables. However, since they track your dive in real time, they tend to be more accurate and allow for longer dives. Every dive should be attempted with a dive plan coordinating the intended depth, time, required stops, nitrogen level, and use some kind of device to stay on top of the schedule. Computer display screens will show MDT, SIT, and specified stop intervals. Scuba divers should become familiar with specific terms used in dive tables and mirrored in dive computers:

Maximum Dive Time (MDT): This is the maximum amount of time you can spend at a specific depth without performing a decompression stop on the way back to the surface.

Decompression Stop: The buildup of water pressure as you descend causes nitrogen from the air you take in to dissolve in your bloodstream. When the buildup gets to a certain point, you will need to ascend slower or take decompression stops to prevent decompression sickness (DCS). Pause during your ascent at a specific depth for a certain period of time to allow for nitrogen off-gassing.

- Precautionary Decompression Stop: Stop for 3 minutes 5 feet/15 meters below the surface as a safety precaution, even if you have not exceeded your MDT. Regardless of time and depth, you should perform a safety stop on every dive.
- Required Decompression Stop: A decompression stop just below the surface (as described above) is required when you exceed your MDT. You may also need to stop at other depths before this final one on deeper or longer dives.

Actual Dive Time (ADT): Similar to a running stopwatch, this is the time elapsed from the beginning of your descent until your return to the surface. You do not have to include safety stop times.

Letter Group Designation: On a traditional dive table, letters represent the amount of residual nitrogen left in your body. The more time spent on the surface, the closer to the beginning of the alphabet your letter will be. Some computers will include a chart corresponding to the original alphabet scale.

Surface Interval Time (SIT): This is time spent on the surface between dives. Your body will be emitting excess nitrogen, and inching up letter groups.

Residual Nitrogen Time (RNT): Before a planned repetitive dive, you must consider RNT as dive time already spent. It is based off lingering nitrogen in your system form earlier dives. Repetitive dives include any dives you make prior to being entirely off-gassed from the previous one.

Adjusted Maximum Dive Time (AMDT): This is your new MDT for a repetitive time at a given depth. If your computer does not calculate this automatically, it is your original MDT minus your RNT.

Total Nitrogen Time (TNT): After a repetitive dive, add your RNT and your ADT together to figure out your new letter group and nitrogen levels.


Any dive computer you use should include some common features. Some devices feature a strap or clasp that connects to your buoyancy compensator. Others come in wristwatch form.

Dive Computers: Dive computers need an easy-to-read display to provide ample information. Screens should show no-stop limits, depth, time, remaining no-stop time, ascent rate, emergency decompression notices, and retain previous dive information. They should include a low-battery warning and be enriched air compatible, meaning they still function with tanks with a higher oxygen content. Some optional features include:

- Air integrated displays to show how much air your have in your tank. Some devices connect to your regulator with a hose, others come with an easy disconnect set-up, while different models use a transmitter on the regulator.
- Combined dive watch and computer mechanisms in one unit.
- Adjustment for altitude diving (either automatic or manual).
- Replaceable or rechargeable batteries.
- Multiple gas computers, or a closed-circuit rebreather mode, for technical diving.
- Download-ability to your regular computer.
- Built-in thermometer or electronic compass.
- Automatically-adjusting decompression models.
- Menu selections with games available for passing the time during decompression and cautionary stops.
- Mask interfaces that let you glance at important information easily.

Dive Watches

Most modern dive watches come with all the major functions of computers in a wristwatch style. They are typically multifunctional, and provide no-stop dive limit information. Some will also come with depth gauges, thermometers, compasses, tide predictors, and dive logs. They always show elapsed time with a quick glance, and are depth-rated for at least 100 meters/300 feet—far exceeding the maximum depth for recreational scuba divers. Extra features include:

- A long and/or expanding strap to fit and clasp over a thicker wetsuit sleeve.
- Automatic winding or solar-powered winding.
- Illumination for reading in low-light conditions.

Choosing a Dive Computer

Dive computers and watches share a multitude of features. When selecting one, keep in mind what kind of diving you will be doing. If you plan on performing many deep dives, or a series of repetitive dives, make sure you have a device with specific functions designed for that. Whether you choose a watch or a computer for scuba diving, ensure:

- Your computer matches or pairs with your diving equipment and/or style.
- The screen remains readable with a mask on.
- The display screen makes sense to you. When tracking ADT, decompression stops, etc., do you prefer a numerical setup or charts and graphics?
- You understand how to access the diving information you need every step of the way.

Whichever device you choose, be sure to read all the instructions for functionality and preference settings. Instructions will also inform you of the best maintenance methods, which typically entail rinsing in fresh water after each use and storing in a cool, dry place away from the sun.

Dependable Diving Technology

In spite of all its necessary equipment, scuba diving remains an accessible activity with a little training. Dive computers and watches make the entire process simpler, allowing you to focus more on underwater sights instead of mathematical calculations. Dive computers should convey all the information you would gain from a dive table in an easy-to-see display. provides a variety of dive computers designed to equip you for all your adventures beneath the water’s surface.

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