For those starting out in scuba diving, there’s a lot of equipment to get familiar with. Mask, fins, regulator, BCD, gauges – and somewhere among all of that you’ll be introduced to a dive computer.
But what does a dive computer actually do? And if you’re a beginner, do you really need one?
Put simply, a dive computer keeps track of your dive and gives you important information to help you dive safely. It monitors where you’ve been underwater, how long you’ve been there and how that affects the amount of time you can spend at different depths without needing mandatory decompression stops.
It sounds complicated. Using one generally isn’t.
What does a dive computer actually do?
Most dive computers are worn on your wrist and automatically start monitoring your dive as you descend.
The display gives you information including your current depth, how long you’ve been underwater and how much time you can remain at your current depth without needing mandatory decompression stops. This is known as your no-decompression limit, or NDL.
Your computer will also monitor how quickly you ascend and warn you if you’re coming up too fast. On a typical recreational dive, it can also guide you through your safety stop.
Depending on the model, it may show water temperature, maximum depth, previous dives and other information.
In other words, rather than trying to keep track of lots of different information yourself, some of the most important figures are right there on your wrist.
How does a dive computer work?
When you dive, increased pressure means your body absorbs more inert gas – primarily nitrogen when you’re diving on air. The deeper you go and the longer you stay there, the more nitrogen your body absorbs.
Your dive computer continually tracks your depth and time and uses a decompression model to calculate your no-decompression limit.
One of its biggest advantages is that these calculations change as you move around.
You might begin a dive at 25 metres, for example, before gradually making your way along a reef into shallower water. Your computer monitors your actual journey rather than simply assuming you spent the entire dive at its deepest point.
You don’t need to understand all the mathematics happening behind the scenes. What you do need to understand is the information your computer is displaying and what you should do in response to any warnings.
That’s something you’ll learn as part of your diver training.
Why does every diver need their own dive computer?
A dive computer is personal to the diver wearing it because it records that person’s individual journey through the water.
Even buddies who stay close together throughout a dive may not follow exactly the same profile. One might be a metre or two deeper at certain points or spend slightly longer at a particular depth.
It becomes even more important when you’re making multiple dives in a day – something you’ll often do on a liveaboard holiday.
Your body doesn’t immediately get rid of all the additional nitrogen it has absorbed when you reach the surface. Your computer remembers your previous dives and surface intervals and takes them into account when calculating the limits for your next dive.
On a liveaboard, where you might make several dives each day over the course of a week, your computer is therefore continually building a picture based on your own diving.
For this reason, divers shouldn’t simply swap computers during a series of dives.
At Emperor Divers, every diver is required to use their own dive computer on every dive. As well as meeting Emperor’s safety requirements, it means the computer can continuously track that diver’s individual dive history throughout their trip.
Do beginners need to buy their own dive computer?
You don’t necessarily need to rush out and buy a dive computer before you’ve even completed your first course.
Dive centres will often have computers available as part of their rental equipment, giving you the chance to become comfortable using one before deciding what you want to buy.
If you plan to dive regularly, however, a computer is one of the most useful pieces of personal dive equipment you can own.
Having your own means becoming familiar with one particular display and knowing where to find the information you need. You’ll recognise its alarms and warnings and won’t need to learn a different computer every time you travel.
It will also record your dives, allowing you to look back at information including depths and dive times afterwards.
What should you look for in your first dive computer?
It’s easy to be drawn towards the computer with the longest list of features, but a beginner doesn’t necessarily need the most advanced or expensive model.
A clear, easy-to-read display is arguably more important. You want to be able to glance at your wrist underwater and quickly understand what it’s telling you.
Simple controls, clear warnings, Nitrox capability and a straightforward safety-stop display are all useful features for a recreational diver.
Some computers have rechargeable batteries while others use replaceable ones, and there are models ranging from relatively simple dive computers to devices that can also be used as everyday smartwatches.
The important thing is finding one that suits the diving you’re actually going to do – and learning how to use it before you get in the water.
A dive computer is there to provide information, not make decisions for you. It doesn’t replace good training, sensible dive planning or your own judgement.
But once you start diving regularly, that little screen on your wrist can become one of the most useful pieces of equipment you own.
Frequently Asked Questions
Do I need a dive computer for scuba diving?
Dive computers are widely used in modern recreational diving because they continuously monitor your depth, dive time and no-decompression limits. At Emperor Divers, every diver is required to use their own dive computer on every dive.
Can two divers share one dive computer?
No. Each diver should monitor their own dive. Even when two buddies stay together, their exact depths and dive profiles can differ. A computer also takes previous dives into account when making its calculations, so it should remain with the same diver throughout a series of dives.
What is the no-decompression limit on a dive computer?
Your no-decompression limit, or NDL, is the amount of time your computer calculates that you can remain at your current depth without needing mandatory decompression stops during your ascent. It changes throughout the dive according to factors including your depth and recent dive history.
Can you use a dive computer with Nitrox?
Yes. Most modern recreational dive computers can be set for Enriched Air Nitrox. You’ll need to enter the correct oxygen percentage before diving and follow the procedures covered during your Nitrox training.
What happens if I exceed my no-decompression limit?
Your computer may tell you that decompression stops are required before you can continue your ascent. Recreational divers should plan to remain within their no-decompression limits and always dive within their training and experience.
What happens if my dive computer stops working underwater?
Computer failures are uncommon, but you should know what to do if yours stops working. Follow the procedures covered during your diver training and the instructions for your particular computer rather than simply switching to or relying on another diver’s computer.
