by Joe Stellini:
You just finished your Open Water Scuba Diver Course and your head is spinning with all the knowledge and skills you have learned. At the top of your list is purchasing what your instructor may have said was the most important piece of dive gear you could own – a dive computer. Your question is, “Why? What is so important about a personal dive computer (PDC) that I should own one?” Most likely that question was answered for you, but here is a little reinforcement to what your instructor may have told you.
First, not everyone wants a fancy, all the bells and whistles PDC, and there are a lot of options out there. Sometimes simplicity means more enjoyment on your dive instead of trying to figure out exactly what you are supposed to be paying attention to on the screen. So getting down to the basics means that there are three things you absolutely need to know during your dive and how to access them on your PDC. They are: Where are you now? How long have you been there? How much longer can you safely stay? This translates into depth, elapsed dive time (EDT), and no decompression limit (NDL). All dive computers have these features, but it’s ease of use and readability that are most important. Everything else is just extra.
To break it down even further, here is why these things are important. Depth obviously comes first because when we plan a dive, depth is one of the first things we set a limit on. Diving within the agreed upon depth limit, whether it be with the Divemaster, your dive buddy, or with yourself on a solo dive, will keep things organized. Not sticking to your planned depth can be confusing and dangerous to all involved. The easiest way to monitor your depth is to learn how to process that information with a quick glance at your computer, often, throughout your dive. If the PDC happens to have an alarm to remind you, even better.
Second on the list, is elapsed dive time. You ask, “Won’t the Divemaster be leading us in and out of the water?” The answer is, “In a perfect world, yes. However in the slightly imperfect world we live in, that does not always work out.” What happens if the group doesn’t want to see what you and your buddy want to see? Or what if you get separated? Or even more common, what if you become too experienced to hang out with a bunch of newbies? You will have to monitor your own time during the dives. Again, an audible alarm for this feature helps. Most dive operations set a maximum dive time and part of being a good diver is following the dive plan whether you or the dive operation set it.
Finally, we have our no decompression limit; last, but far from least. Some computers have audible alarms for this feature as well. When it comes down to it, not following a good dive plan with regard to our two previous features, depth and EDT, could result in decompression illness. Going too deep, coming up too fast, and staying too long, will eventually and most certainly catch up with you. Yes, DCS has been drilled into your head during your open water class and will be addressed even further during any advanced or continued education courses you may take.
So why is NDL important? Because it takes your depths and times during each dive or repetitive dives and calculates how much longer you can safely stay at your current depth. Breaking these rules could cause the loading of too much nitrogen resulting in a mandatory decompression stop. As a new diver, we want to avoid a deco stop at all costs. Your PDC can tell you when to move to a shallower depth, will recalculate your NDL for the new depth, and will do this every single time. Not only does this keep you safely within your nitrogen limit, but it will significantly extend your dive times allowing you to multi-level dive. You can’t get that with dive tables.
The personal dive computer you used in your SDI course was probably attached to the regulator system. If you are not interested in the whole package then consider a wrist-mounted computer. This makes traveling with a PDC lightweight and easy.
On a final note, always remember to monitor your air. Although some PDC’s may be air integrated, divers that do not use one will have to check their pressure gauge every few minutes.
For more answers on personal dive computers please consult with your local SDI Dive Center. They are there to help and provide you with the best customer service possible and should be able to answer all of your questions on personal dive computers.