Dive computers allow us to enjoy longer, safer dives. But have you ever wondered how dive computers work?
If you learned how to plan dives using the RDP Table or The Wheel, you may have a general idea how dive computers work. For those who didn’t learn how to use a dive table, here’s a quick overview:
“RDP” stands for Recreational Dive Planner. The RDP Table and The Wheel helped divers estimate how long they could stay at a given depth without making a decompression stop. The RDP Table also helped divers decide how much time to spend at the surface before making another dive.
To plan a dive, you’d start with your planned maximum depth. Let’s say you want to dive a wreck sitting in 24 meters/80 feet of water. You’d find 25 meters/80 feet on the RDP Table and draw your finger down the column to see how much time you could spend at that depth without making a decompression stop. This is also known as your no decompression limit (NDL). For that wreck at 24 meters/80 feet, your maximum dive time is about 25 minutes.
“But I’m not going to just drop to the bottom, swim around and come back up,” you might say. “What about the time I spend swimming around the top of the wreck?”
Planning a dive that starts at one depth and then moves to another is called a multilevel dive. The Wheel, and later the eRDPML, allowed divers to plan multilevel dives. But using a dive computer is significantly easier.
The magic box on your wrist or in your dive console is like a super-charged version of The Wheel. It constantly recalculates your NDL based on the actual time you spend at the base of the wreck, swimming around the top of the wreck, etc.
Computers don’t follow the RDP Table exactly, but each one has an algorithm based upon the same scientific principles. The video below from diving expert Jill Heinerth explains the scientific theory of how dive computers work.
Dive computers use real-time data from your dive to estimate how much gas your body tissues are taking in and releasing throughout the dive. Because the human body is made up of different types of tissue (blood, fat, organs, etc.), the computer has no way of knowing how much nitrogen is actually in your body. Instead, it uses theoretical tissue types, known as compartments, that absorb and release gas at different rates. Some computers use an algorithm based on 16 different tissue compartments.
Dive computers also factor in previous dives and calculate residual nitrogen. For example, if you have a 60-minute surface interval, the computer might estimate your fast tissues have completely off-gassed, while slower compartments still contain varying levels of nitrogen carried over from your first dive.
Dive Computer Technology Over the Years
The first dive computers designed for recreational divers debuted in the 1980s. Early models had one mode and were the size of a small smartphone.
During the 1990s, manufacturers added new features such as:
- Air integration
- Ascent rate indicators
- Modes for Nitrox and other breathing gases
Today, divers can buy dive computers the size of a smartwatch that display custom alerts, remaining dive time based on air consumption and much more.
Dive Computer Limitations
A computer is only as smart as its user. For example, on my first trip to Cozumel, I dove Punta Sur (Devil’s Throat), the island’s most famous deep dive. While ascending, my computer started to flash: Ceiling, Ceiling, Ceiling.
“That’s weird,” I thought. “I wonder what that means. I hope it’s nothing bad.”
Why am I telling you this embarrassing story? Because I never bothered to read my computer’s user manual. I bought a beginner-friendly dive computer the dive shop recommended, strapped it on and went diving.
If I had looked at my dive computer’s manual, I would have understood I needed to stay below a certain depth to avoid a decompression injury. I was very lucky I didn’t get injured that day.
Even if you know what “Ceiling” means, the point of the story is that a computer isn’t going to keep you from getting injured underwater. For example, divers who adjust their computer’s settings to be less conservative may think, “I’m just increasing my dive time.” But they may also be increasing their risk of a decompression injury.
A dive computer doesn’t know your age, fitness level or if you drank too much last night. The medical experts at DAN (Divers Alert Network) note:
“Divers are often surprised when symptoms of DCS develop after dives that were conducted within the limits of their dive computers. It is important to remember, though, that while mathematical models predict outcomes, they do not guarantee them. The fact that a dive was conducted within the limits suggested by a dive computer (or a dive table) does not make a DCS hit ‘undeserved.’ The mathematical algorithms provide guidance that must be evaluated and tempered by a thoughtful diver.”
Curious About How Dive Gear Works?
If you want to learn more about how dive computers work, how regulators work, and how to ensure your dive gear lasts as long as possible, sign up for the PADI Equipment Specialist course. You’ll also learn how to make basic gear repairs and get one step closer to becoming a PADI Master Scuba Diver.
