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March 2022    Download the Entire Issue (PDF) Available to the Public Vol. 48, No. 3   RSS Feed for Undercurrent Issues
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Backup Computers, Part III

Master the complexities

from the March, 2022 issue of Undercurrent   Subscribe Now

After two parts of our article on backup computers, we've established just how important it is to use them correctly. If your main computer fails, you have a backup to continue diving safely as well as the data required to conduct follow-up dives.

A divemaster insisted his wife's Suunto showed mandated deco when it was merely counting down a safety stop.

As our readers' reports have demonstrated, computer technology has vastly improved, though it's still not perfect, as air-integrated technology can still have some issues.

And then, for aging divers, the technology itself can get a little tricky, at times baffling. When we don't understand a problem with our laptops or iPads, some of us have learned to call our kids or maybe grandkids for help. Underwater, we're on our own.

Here's the last in our three-part article on backup dive computers.

Are Modern Computers Too Daunting For You?

Today, any device with computer chips can have so many operating options it can be daunting for some people. For example, automobiles may offer collision avoidance, lane discipline, auto light-switching. However, some drivers never get used to them and stick with the basics: an accelerator, a brake pedal, a steering wheel, and a PRND lever, never coming to terms with the more sophisticated and safer options.

Dive computers, too, have basic functions: depth, time, ascent rate, no-stop time; but today's computers can do much, much more: Some can display your heartrate and others even let you play computer games while waiting out a deco stop. Others let you preprogram multiple gas mixes including those with helium. While many divers spend a great deal of time understanding what their computers can do, others stick with the basics. But even the basics one must master.

Too often, when a diver uses a new computer, rents or borrows one, he fails to understand the display fully. John Miller of Texas Dive Center was critical when he wrote, "I don't know many divers who know how their own dive computers truly work. So how are you going to rent one on a trip and learn it the day before that first dive? A dive computer is the first piece of equipment every diver should purchase and then learn how to operate." (See Undercurrent September 2021 "Understanding Your Diving Computer")

Even divemasters may not be familiar with some computer displays, as Paul Martin (Ashville, NC) discovered when a divemaster insisted his wife's Suunto was showing mandated deco after a 35-foot dive in St. Croix when it was merely counting down a safety stop.

Some divers are daunted by complexity. On the other hand, some love the extra possibilities of sophisticated computers. Douglas Franquemont (Colorado Springs, CO) dives with two Shearwater technical diving computers. He says, "I make sure all parameters are set the same on each, most notably the gradient factors. Besides simply having a backup, I set each computer to display different information during a dive, so at a glance, I can see everything I need (and more!) without having to push any buttons."

Ken Hayduck (Angola, IN) uses two Shearwater computers. "It is common for me to be holding a surface float reel, two lift bag reels, a mesh bag clipped to my BC with bottles and assorted treasures, a rod and reel in one hand and a paddleboard paddle in the other, and reading a screen regardless of which hand is busy."

Even simple computers can seem over-complicated. Rod Ellis (Smithton, MO) suggested, "The Oceanics [which replaced an earlier Sherwood Courier] are a bit less intuitive and easier to read than the old simple Sherwood. The latest Nitrox unit has a bit too many whiz-bangs or complicated button-pushing. There are defaults and resets to monitor or adjust."

If the latest computers are too daunting, you may be tempted to pick up an older, secondhand, simpler model. Gareth Richards (Loveland, OH) recommends this. He always dives with a backup. "All are identical brands to minimize confusion with differing readings, and there's only one method of operation to learn. It's easy to pick up another used computer for a reasonable price. I have no problem buying used computers. They work, or they don't, so it's easy to have confidence in them. There are many available, almost new for low prices. Perhaps people did a little diving and then stopped."

Be aware that dive computers get stolen and often turn up on eBay. Suunto has had a policy of buying all current computers so advertised. They have a serial number and a history, so they can be traced back to their source - so a bargain may turn out to be money lost.

Craig Capehart (Carmel, IN) likes old-style Mares Puck computers. "My two are identical, although one face lights up (but not bright enough to read at night at depth). Each has only one button, so I don't need to remember any combinations of button pressing."

One diver told us he did not carry a backup because he found it too cumbersome and one more thing to deal with in a life of endless maintenance tasks - although we would argue that rinsing it in fresh water and pressing its buttons after a dive wasn't that onerous.

In September, we wrote about a woman we called Anna who went on a liveaboard trip aboard the MV Aqua in the Galapagos. An inexperienced diver, she rented her computer on the boat and didn't fully understand it. One day, during her safety stop at the end of her second dive, she showed her computer to the dive guide; it displayed arrows pointing downward and an 18-minute minimum ascent time. She did not understand what the rented Suunto Zoop computer was telling her. Regardless, the guide indicated she all should surface, which she did, missing the mandated deco stops displayed.

Later, the dive guide told her to ignore her computer "because Suunto Zoops were overly conservative." She got seriously bent and had to be evacuated. As we wrote earlier, stick to the information offered on your own computer. Always.


Thanks to all our subscribers who have told us about their computers, their backups, and how they use them. You have provided some simple rules for backup computers:

  1. Master the manual, and understand the display.
  2. Always carry two with identical algorithms so that your backup has not gone into error mode while you were managing your dive on a different algorithm.
  3. Keep them well maintained, with fresh batteries or fully charged batteries.
  4. When your computer tells you to ascend or stop, do it, and ascend at the prescribed rate displayed.
  5. It's essential to take your backup computer along with you on every dive, as Simon Carolan (Blackrock, Eire) reminds us, "There is no point in keeping your backup computer on the surface. It has to do the same diving as you so that it knows what your nitrogen loading is."

- Ben Davison

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