A Buyer's Guide to Dive Computers

Those faced with buying a dive computer today have a bewildering supply from which to choose. Where do you start?

Well, you can start with this article! First of all you should know that all dive computers have the following basic functions: track total bottom time and maximum depth reached on each dive and display or allow this information to be accessed for at least the last dive; track and display surface interval time; calculate and display no decompression time limits by depth for your next dive; calculate and display time that must elapse before you fly; visual or audible alert that you are ascending too fast; guidance through an emergency decompression situation; and a battery low power display or icon. While these are the basics, almost every dive computer on the market offers numerous other functions and features, some of which will be important to you and some that will not.

There are three basic types of dive computers: watch style, module (for wrist, console or hose mount) and air integrated. Choose one you can afford that offers the features you want.

Watch style: These multi-function instruments resemble large watches and are worn on the wrist. They perform all the functions you need and expect from both a watch and a dive computer. While you get two instruments in one, keep in mind the numbers/letters on the display may be too small for older eyes to read under water.

Module: These computers are among the most economical on the market. Many are round and have just one button, which turns them on and accesses all of their functions. Another common form is rectangular, with contacts that access the functions. Both are available in consoles; wrist and/or hose mounts are also available for many.

Air integrated: There are two kinds of air integrated computers: those that connect to your regulator via a high pressure hose and those with no hose.

Air integrated with hoses: These replace the submersible pressure gauge on the end of a high pressure hose and, in addition to providing a dive computer's usual functions also provide information on your air supply, including an estimate of how long it will last. I love mine, but when I travel overseas I bring a backup console with an SPG. The computer has never stopped working under water but it has failed to function properly on the surface. (I also always dive with two computers.)

Air integrated hoseless: These are among the most expensive dive computers you can buy. They consist of a wrist or BC mount instrument, which is the receiver, and a transmitter, which screws into the high pressure port of the regulator first stage. The transmitter sends information on your air supply (via radio signals) to the receiver, which displays it.

Features

Dive computers offer a humongous number of features. Here are just a few:

Automatic activation: Some computers turn themselves on when they are submerged to a particular depth, others must be activated by pushing a button, touching a contact or two with wet fingertips or turning what is called a battery door. If you think you might be prone to forget to turn your computer on, buy one that turns itself on. Some will not work under water if they have not been activated on the surface first.

Batteries: Some dive computers have a user replaceable battery or batteries, others must be returned to the factory or an authorized dealer for battery replacement.

Memory: Many, but not all, dive computers retain their memories if the battery(ies) has to be changed in the middle of a dive day or trip. If you make a lot of multi-day trips, you want a computer that retains its memory through a battery change.

PC downloadable: A great many computers can download their information into your PC using an optional interface. If this is important to you, look for this feature.

Nitrox capability: While all nitrox computers can be used to make air dives, an air computer must be nitrox programmable in order to be used with this breathing gas (it contains a larger percentage of oxygen than air). There are now air computers on the market that can be upgraded to nitrox computersyou can use them for air dives now, if and when you become nitrox certified the computer can be quickly upgraded for use with that breathing gas.

Decompression capability: All computers on the market will guide you through an emergency decompression situation. Many, however, are not intended to be used for planned decompression dives. If you think you might be interested in tech diving, this is something to keep in mind when choosing a computer.

Illumination: Many but not all dive computers have faces that glow or illuminate for easier viewing in low light conditions. If you are a wreck, cave or tech diver, this feature is important.

Varying profiles: A few computers allow the user to make them more or less conservative with different altitude programs (some have as many as four from which to choose). Most computers today are already conservative, this features makes them even more so and adds a safety margin. (But keep in mind that no computer can guarantee you will not get bent.)

Price Dive computers today are available for just less than $250 to in excess of $1,250. When shopping, take your time, look at everything, then buy what you need and want. If you can afford and want that top of-the-line, all-the-bells-and-whistles-model, go for it. If you're on a budget, an economy model will probably more than meet your needs.

FAQs (Frequently Asked Questions)

Q. Are the more expensive computers safer than the less expensive ones?

A. No. All dive computers are safe when used as intended. Conversely, no computer is safe if it is used with reckless disregard for safe diving practices. For instance: a computer will "let" you make a shallow dive followed by a deep dive or several deep dives in a row. You know from your dive training, however, that this is not safe and should not be done. If you violate dive laws you will suffer the consequences no matter what dive computer you use.

The difference between expensive and not so expensive computers is sophistication; the more expensive the computer the more it offers.

 

Q. Do I need a computer with lots of features?

A. That depends. Most computers offer many more features than most people will ever use. Almost all, for instance, offer high altitude capabilities. Few people, however, ever use their computers at high altitudes. Make sure the computer you buy has all the features you need and want, consider the extra ones icing on the cake.

The day the Aeris Savant computer was delivered to our office I pulled the manual out of the box and braced myself, expecting to read some poorly translated instructions resembling an indecipherable cross between several languages I don't speak. To my surprise, the directions were clear and made sense!

The Aeris Savant is a wrist-mounted nitrox computer, programmable for mixes ranging from 2150% oxygen, with large, easy-to-read characters. Following the instruction manual, the Savant appeared to be very simple to use and to program, yet it has enough features to satisfy even the most information-hungry divers (see table: "Savant Features at a Glance").

Sitting in an office with manual in hand is one thing, but being able to program a computer at a dive site is another so I took the Savant for a number of dives, both shallow and deep, for the real test. Programming the Savant for a specific mix takes no more than thirty seconds and the default is 21% (air), which means that diving air would require no programming at all. My first dive using the Savant was when I was helping out with a beginner scuba class. I programmed the computer and went to help the students with their equipment. I made the mistake of not double-checking the computer settings when we finally entered the water and, during the dive, I was very surprised to see that the Savant was calculating my decompression status at the exact same rate as my air computer! It turned out that the computer had defaulted to 21% O 2 since it took me so long to get into the waternot really a problem since this increased my safety margin. Also, this being my first time diving with a wrist-mounted computer, I realized that in order to prevent the computer from sliding around during the dive as my suit compressed, I had to tighten the strap to the point where the circulation in my hand was cut off until I began my descent. I'd be interested in knowing what other divers do to compensate for this (Hint: Readers write in with your tips!).

On subsequent dives, I had more of an opportunity to gauge the Savant's performance. The back-lighting came in very handy, as did the graphs which provided me with a constant update on my status in terms of nitrogen loading and my O 2 clock. On the whole, this is an excellent nitrox computer for recreational divers, and since it is so easy to use, even those divers who have stayed away from using computers and/or nitrox should be satisfied now. And for those who are concernedit is Y2K safe.

For more information about Aeris products or to find the name of an Aeris dealer near you, contact Cross Country Parts at: Phone (403) 235-5454 or fax (403) 235-6394.Catherine Adler