So you want to know a little more about dive computers. No problem! This is an article for brand new scuba divers who are in the process of getting their scuba certification, or divers who have never used one before about how to use personal dive computers (PDCs) underwater.
What do Dive Computers do?
Dive Computers have different features, alarms, and notifications, but they all have basic functions. Check out the picture on the right. While underwater, a dive computer in “dive mode” will tell you the following information…
- Your Current Depth (top number)
- Dive Time Remaining (middle number)
- Your Current Nitrogen Level (the bar graph on the sides of the computer)
- Your Dive Time Elapsed (bottom right number)
Why is this important?
Divers have to be able to determine with accuracy how much Nitrogen is in their body at any given time. Back in the day, divers used to have to use a dive table to determine this. Pictured left, this dive table would guide a diver through manual calculations to a hardline time limit of how long they could stay at a given depth. This time limit is also commonly referred to as the No Decompression Limit. With a dive table, it didn’t matter if you touched your maximum depth for 2 seconds, 2 minutes or 20 minutes. Your total dive time was pre-determined, unless you did an entirely separate calculation using the table for a multi-level dive. Sound tedious? It is!
For example, if you are planning a 50 foot dive, and you drop your GoPro or light, you can go to 60 feet to pick it up briefly. When diving with a table, you would have to calculate for a 60 foot dive. On the other hand, dive computers are a foot by foot No Decompression Limit calculator. So if you come back shallower, it will recalculate and extend your No Decompression Limit to reflect your current depth. Remember to check your computer constantly to monitor both your current depth and your current No Decompression Limit. Once you go beyond it, you have now entered Decompression diving and have placed a virtual ceiling over yourself. Now you must make mandatory stops as you ascend. These stops can sometimes be 10 minutes to hours at a time, and if skipped, will likely result in Decompression Illness.
Unplanned Decompression is dangerous.
Decompression training is not covered in standard Open Water or even Advanced coursework. The recreational diver would be wise to avoid these technical challenges.
The bar graph is a real time display of how much Nitrogen you have in your body. The bar graph takes a longer time to change than the foot by foot No Decompression Limit. Checking the Nitrogen bar can help you decide if you want to do a longer safety stop or surface interval to reduce risk.
Your total dive time after repetitive dives (multiple dives within 24 hours) will play a factor in all the calculations. Keep track of your total dive time.
Dive Computers While Ascending
Another important feature of the dive computer is the ascent alarm. You can find it on most computers on the side of the screen. It is usually represented in arrows. Some newer models have color coding, and even auditory beeps. Ascending Slowly is one of the 3 major rules of Scuba Diving, so it is a good practice to CYA – Computerize Your Ascent. Always periodically glance to make sure that you are not going up too fast.
I like to wear my computer on my right wrist, so that I can let air out of my BCD with my left hand. This way I can still easily see the screen.
Sound travels 4.3 times as fast underwater as it does through the air, and that makes it difficult to determine its direction. Therefore, it’s a good policy to check your computer if you hear any kind of beeping. It may be yours.
See the ascent alarm on the right hand corner of the screen. This diver is making a safe, slow ascent.
This safety stop has 2 minutes left on its obligation.
Safety Stops on Dive Computers
A safety stop is a precauationary method that is strongly recommended for every dive. When a diver is on their ascent, the computer will switch from regular dive mode and display the safety stop. It will most often appear as a countdown from 3 minutes. While the recommended safety stop for most computers is 15 feet (5m), safety stop mode is active in a range of anywhere between 12-20 feet (4-6m). If you exit the given range of safety stop for your computer, it will go back into dive mode. You will need to get back into range to resume the stop counter.
You can see the computer on the left has reached 2 minutes left of the safety stop. On that particular model, it has replaced the No Decompression Limit in the display. Having the safety stop prominently featured is convenient, but it might not always be the case. You may have to look around the screen to find out just how much of your safety stop obligation is left. When you have your own, you know where to find it every time.
It is important to note that many computers will not make you do a safety stop if you have not descended below 40 feet, but there is no reason why you cannot do one manually by taking note of your total dive time and adding three minutes. You may have to do this if your safety stop mode is not turned on prior to the dive.
Be sure you understand your computer, its features and functions prior to taking it underwater.
Once the safety stop is completed, the computer will revert back to traditional dive mode, and you are now “clear” to ascend to the surface.
Additional Features of Dive Computers
Dive computers have other functions as well: Dive Planning, Mixed Gas use (Nitrox), Countdowns to Safe Flight, Logbook, as well as additional alarms. Some popular alarms are: turnaround time, dive time remaining, maximum depth alarm, and ending dive time.
As technology progressed, computers evolved to include air integration, allowing divers to monitor the air in their tank on their PDC. This cohesion allows the computer to give the diver more information such as an air consumption rate, turnaround air alarm, and when to safely start their ascent.
Every generation of computers that comes out has additional features, but they are made to last. A personal dive computer purchase can last a diver many years if properly maintained. And as a diver progresses in their training, they may decide to relegate their once main computer to a backup role. Personally speaking, my old dive computer is attached to my camera housing tray, so I can always make sure I never go too deep when seeking a turtle shot on a wall dive.
Any purchase of personal dive computers from Scuba Network comes with a tutorial from an instructor. Secondly, if you forget how to use it or take a new class and want to unlock more advanced features, come back. We will sit with you and teach you all over again.
It’s such a huge bummer for me when I buy something and have to spend hours deciphering a poorly laid out picture manual, or digging up videos on the internet to try to understand what I just purchased. That’s why I think that if you buy something from a dive shop, it is our responsibility to educate you on how to use it. Above all, we prefer to be scuba diving educators as opposed to salespeople.
