How to Use a Dive Computer [Without Any Experience]

Rok Valencic

If you’re in the market for the best dive computer or will be renting one for the first time, it’s important to know how to use a dive computer correctly. After all, it’s your safety at stake here. Or maybe you’re old-school and switching over from dive tables.

When I got a rented dive computer handed to me the first time with five-second instructions, I didn’t think much of it. I ended up exceeding my maximum depth and missing the decompression stop. It wasn’t the best dive computer for a beginner, but still.

But I’ve learned from the experience, and now I’m here to make sure you do better!

Why Knowing How to Use a Dive Computer is Important!

Before we dive into this guide, I’m assuming you know what a dive computer is. If you don’t, read about what are dive computers so you’ll know the basic functions and features I mention here.

It’s all about your safety underwater. When you’re scuba diving, you rely on that little gadget to keep you in check with things like depth, dive time, and decompression limits. If you don’t know how to use it properly, you could end up in some risky situations.

Imagine this: You’re down there, having a great time exploring the reef, but if don’t know how to read it properly, you might unknowingly go too deep, stay down for too long, ascend too fast, or miss a decompression stop. That’s when problems can start to bubble up, like decompression sickness or even worse.

Plus, knowing your dive computer means you can enjoy your dive more. You’re not constantly stressing about your depth or time because you trust this important piece of dive equipment to give you the right info. So, take the time to learn how to use it right – your underwater adventures will be a lot smoother and safer.

How to Read Dive Computers?

As someone who has used and tested over 50 different dive computer brands and models over the past years, I can tell you that no two are exactly the same, although the interface usually follows some similar logic.

That’s why I’ll be using two different dive computers throughout this guide to show you the slight differences (and similarities) between different computers and to best prepare you for whichever computer you’ll actually be using yourself.

A dive computer display during a dive

Above, you can see what Shearwater Teric (a high-end computer watch on the left) and Mares Puck Pro + (a good entry-level computer on the right) show on displays in dive mode using air. Other devices that fall into the best dive computer category will function similarly.

All decent dive computers will show you the most important dive information that I also pointed out in the image:

  • Current depth: so you know how deep you are and don’t go too deep (both examples show depth in meters, but units can be changed to feet on any computer).
  • Ascent rate: both examples show a number of feet/meters per minute and a graphical representation of the ascent rate. The Teric uses arrows (more arrows = greater ascent rate) and changes color or flashes if you ascend too fast. The Puck Pro shows a black arrow along the left edge if your ascent rate exceeds the recommended values.
  • No decompression limit (no-deco or NDL): how long can you remain at your current depth without the need for a decompression stop. This is always expressed in minutes.
  • Dive time: the total dive time from the moment you enter the water. Most computers automatically enter dive mode as you start descending (usually around 3-5 feet deep).

There is one more piece of data that I would classify as important: safety stop information (or decompression stops). Both computers show that as well, but only if such a stop becomes necessary during a dive. I’ll get to that in a minute.

As you can see, there are slight differences in what and how computers display information, but it’s quite simple once you know what to look for.

Additional Dive Info
Each computer will show some additional info, like water temperature, maximum depth, estimated time to surface, dive mode, etc., but nothing vital to your dive. If you pay attention to these five things I mentioned, you will be well-equipped to monitor your recreational dive safely.

Now, let’s get to how you set up the computer before beginning the dive.

Pre-Dive: Set Up and Planning

If you will be diving with your own computer, read the user manual. This may seem obvious, but a lot of times, divers miss some important information because they skim through the manual too quickly or don’t read it at all.

If you’re renting a computer (or using your own), make sure to check the following things before starting a dive:

  • Are you using units that you can understand (feet or meters)?
  • If you are diving at an altitude, the altitude must be set to make sure the depth readings are correct. You most likely won’t be if you’re a beginner, but it’s good to have this in mind.
  • Is there enough battery life to last through the dive (or multiple dives and the time between!)?
  • Set the correct dive mode. Most computers allow diving in multiple modes, but recreational open-circuit is always the default mode. If you’re a beginner recreational diver using air, then you most likely don’t need to change anything.
  • How to turn on the backlight. Even if you’re not diving during the night, it might be early morning, evening, low visibility water, or you have poor eyesight, and a light can help. In dive mode, this usually means pressing a button. For example, it’s the top left button on the Teric and holding the button on the Puck Pro.
  • It’s good to know what each button on the computer does. Even if you don’t need anything, you might accidentally press something underwater, and it’s good to know how to get back to the correct display.

This is it! I’m assuming you will be scuba diving recreationally using air, so you don’t need any other settings.

Now, you’re ready to start the first dive of the day. I’ll also guide you through the process of getting ready for subsequent dives. But, one thing at a time.

Right or Left Wrist?

To be completely honest, this is, in most cases, irrelevant.

This is more a personal preference than anything else. If you’re used to wearing a watch on the left wrist, then wear the computer on the left wrist as well.

Some divers prefer to wear it on the right because the pressure gauge and the inflator are on the left, and they like the option to be able to purge air and use a computer at the same time. But if you’re a beginner, I suggest you don’t worry about this.

If you wear the computer on the left wrist and go from having your left arm below you to suddenly purging air above your head, the computer might freak out for a second because it can measure that as a fast ascent rate, but this is nothing you should worry about either.

How to Use a Dive Computer During a Dive?

Your computer will be all set once you enter the water. After that, all you must do is read the display and turn on the backlight if needed.

Activating the Dive Mode

Dive mode will activate automatically as you start descending, usually somewhere between 3 and 6 feet deep.

If you’re worried, some dive computers allow a manual dive mode activation.

For example, the Shearwater Teric also has a regular watch function, and you have to press the menu button and select Dive to enter the mode. But as I said, the watch does it automatically as well as you start descending.

Enter the dive mode on display of the Shearwater Teric

On the other hand, the Mares Puck Pro + will always switch on in pre-dive mode, and there is nothing more you can do to force-start the dive mode. Dive mode starts as you enter the water and start descending, as it does with all the top-rated dive computers.

Reading Descent Information

All the data on the screen will keep updating with increasing depth.

Keep in mind that dive computers have a sample rate of 5-10 seconds, which means they will take measurements and change the values on the display at the same frequency.

If you immediately descend to your maximum planned depth, you will obviously keep an eye on the displayed depth to know when to stop. Otherwise, you will only be checking the computer now and then to see what depth you’re at and how long you can stay there.

Which brings me to the most important function of every dive computer: calculating your no decompression limit or your decompression stops.

Monitoring Depth, Dive Time, and NDL

As you know from your dive course, the deeper you descend, the less time you can stay there without having to make a decompression stop.

Depending on your dive plan, there are two possible scenarios:

  1. you will dive only within NDL (so no decompression stops),
  2. or you will go deep enough or stay down longer and make decompression stops.

Diving No-Deco (NDL)

As soon as you start your dive and descend to a certain depth, the default display will show you the NDL in minutes:

NDL displayed on a dive computer

This means you can stay that long at your current depth without the need for decompression stops.

If you continue to descend or ascend, the dive computer will keep recalculating and updating the NDL, always showing you the time for the depth you’re currently at.

All you need to worry about, in this case, is not exceeding this time limit.

If You Exceed the NDL
If you exceed the NDL for whatever reason, don’t worry. That only means you will have to make a decompression stop on the way up, even if you didn’t plan one. DO NOT miss or ignore this stop! As soon as you exceed the NDL, the NDL information will be replaced with information about your safety stop.

Even if you dive within the NDL, you must still perform a safety stop between 10 and 20 feet (3-6 m) of depth for 3 minutes. All dive computers automatically calculate a safety stop into your dive as soon as you drop below 33-35 feet (10-11 m).

Safety Stops and Alarms

Whether you need a safety stop or a decompression stop, the process of reading the dive computer, in this case, is the same.

If you exceed the NDL, the dive computer display will change the NDL information to show the stop information instead. All dive computers do this automatically.

Dive computer displaying deco dive info

There are three new pieces of information displayed now:

  • the depth of the required stop
  • the duration of the stop
  • and the total ascent time, including all stops

Everything will be done automatically. The only thing you need to worry about is actually making the stop, which means going to the required stop depth and remaining there for the duration displayed on the display.

The safety/deco stop timer will start automatically as you reach the required depth. Safety stops will always count down minutes and seconds, while deco stops display only minutes.

The difference between a safety stop and a deco stop on a dive computer

As you complete the stop, some high-end dive computers will indicate that the stop has been cleared, while others will just remove all stop information altogether.

Either way, as the time for the stop reaches zero, the stop is cleared, and you can continue your ascent.

In case you ascend higher (or descend lower) than the recommended stop depth before the entire stop time has been cleared, the timer will pause. Usually, some graphical warning will be displayed if that happens:

Safety Stop and Deco Stop paused on a dive computer

This varies between computer brands and models. Some will only graphically let you know that the stop is paused (like the Teric on the left) and assume you know that you went out of the required depth range (which is the only logical explanation anyway).

On the other hand, some won’t graphically note that the timer is paused (like the Puck Pro on the right) but will show you that you’re too deep or too shallow, usually with arrows pointing the way you should go (up or down).

Heads Up!
Your dive computer is a tool, not a scuba diving instructor. If you miss a stop or don’t complete it, there is no lock-out or penalty. It’s up to you to keep track of the necessary stops and make sure you actually complete them.

Another important thing to note is that dive computers recommend safety stops, but they are not mandatory.

So, while some more high-end computers, like the Teric, will pause the safety stop timer and display the pause if you go outside the stop depth range, some computers will assume you decided to skip the safety stop and stop displaying it altogether.

This is different for decompression stops because they are mandatory, and the stop timer won’t just go away unless you miss the entire stop for a longer period of time. And even then, you’ll see a warning.

Pro Tip
Remember that having a computer allows you to take your mind off things and enjoy your dive more than you could without a computer. So even if you’re a little bit nervous about using one the first time, try to relax and keep your eyes on the underwater world, not glued to the display.

Checking on it with the same frequency as you check your pressure gauge is more than enough to stay within the NDL and catch all the stops.

(Optional) Deep Safety Stops

Some dive computers also include deep stops in their decompression algorithms, but this depends on the model. For example, the Mares Puck Pro + has them, while the Shearwater Teric doesn’t.

If your dive computer shows you a deep stop during your dive, then perform one.

This is still ongoing research, and dive professionals have different opinions on deep safety stops. Deep stops aren’t mandatory, and dive computers with such stops will treat them as ordinary safety stops, just at a different depth.

This is what a deep stop looks like on the Puck Pro:

Deep stop displayed on Mares Puck Pro +

First, the depth of the deep stop is shown as you approach the end of the no-deco limit. Or, in the case of deco diving, the deep stop is shown as the first deco stop.

As you reach the required depth, the timer automatically starts, and the process is the same as that of the regular safety stop.

Ascent Rate Monitoring

This is one of the things that is constantly displayed on the display or shows as soon as you start ascending, and you don’t have to worry about it until you start your ascent.

You don’t have to keep track if your ascent rate is below the recommended value (30 ft or 10 m per minute). Just pay attention to any warnings indicating that you’re going too fast and slow down if that happens.

Ascent rate alert on a dive computer

Color dive computer displays will show a yellow, orange, or red reading if you ascend too fast. Monochromatic displays will start blinking and display additional indicators, like the flag along the left edge of the Puck Pro.

Take these warnings seriously because ascending too fast is an easy way to get the decompression sickness!

What to Do Post-Dive and Between Dives

There are three things to do after you finish your dive:

  1. Rinse the dive computer with fresh water
  2. Transfer the dive log to your phone or computer
  3. Plan your next dive of the day

The first one is fairly obvious: you want to get rid of the salty water on your computer, which is corroding any metal contacts and sticking up moving parts.

If you want and have the option to do so, you can transfer the log of the current dive to your device and review it, adding any comments. This isn’t necessary, but I find it helpful for spotting patterns in your personal dive experience and better planning future dives in the long run.

Regardless if you’re plan is to make more dives soon or not, there is some information the computer will show that you want to know:

  • The remaining desaturation time to complete off-gassing
  • No-fly time
  • Nitrogen load
  • NDL times for different depths for repetitive dives
Post-dive display on a dive computer

This is something that each dive computer will do differently.

Some dive computers will show the remaining desaturation time and the nitrogen load, but won’t have dive planners for subsequent dives (so no NDL depths, like the Puck Pro on the right). Or they will have a dive planner and (usually) no other information (like the Teric on the left – although it also shows nitrogen load on a different screen).

Technically, this all achieves the same thing: it helps you with estimating the time needed to off-gas completely and plan the depth and time of the next dive.

If you don’t plan another dive on the same day, then all you need to remember is not to fly in the next 12-24 hours. Dive computers that show this don’t actually calculate anything but display the no-fly times recommended by reputable diving agencies (which is 12 hours for single NDL dives and 24 hours for everything else).

Planning the Next Dive

If you have a high-end dive computer that includes a dive planer, like the Shearwater Teric, then this will be fairly simple.

When you start planning the dive, simply enter the remaining surface time until the next dive, and the computer will return a table of depths and the maximum NDL time for each depth, already taking into account your nitrogen load from the previous dive.

If you’re diving using only air, then make sure that that’s the only programmed breathing gas in your computer. Otherwise, the computer will recommend enriched air because it’s more optimal for subsequent diving.

Do I Need to Plan?
While dive planning is recommended for safety reasons and experience, you don’t necessarily have to plan anything and can just start the second dive when you’re ready. The computer will automatically go into dive mode again and display the NDL for your current depth again, accounting for the nitrogen loading of the previous dive (and the surface interval time).

If you’re diving using air and only do NDL diving, then you don’t need to complicate things. I mean, you can still plan the second dive if you’re curious about how deep you can go and for how long, but it’s not necessary.

This applies to all dive computers, whether they have a dive planner or not. All will account for the nitrogen load and automatically enter the dive mode when you start the second dive. Just remember to check the battery life again, set the altitude if relevant, etc.

If you’re set on planning the second dive and don’t have a dive planner on your computer, then it’s the dive tables for you. It’s the only other way to do it, but that has a charm as well 💪

What I usually do is take the maximum depth of my previous dive and the total dive time to find my starting pressure group in the dive tables. After coupling that with the surface time, I can easily estimate the NDL for the next dive.

Should You Turn Off the Dive Computer Between Dives?

NO!

The computer will continue calculating your nitrogen load and off-gassing during the surface interval, which is very important information to know during the second dive.

If you were to turn off the computer or take out the batteries, then the computer might not calculate your surface time and off-gassing correctly, which would result in wrong NDL times and decompression stops.

That can, in turn, lead to decompression sickness, so… just no.

Tips on How to Best Use a Dive Computer

If you do all that I’ve talked about so far, then you’ve basically covered everything for recreational open-circuit diving.

All I can add is play around with your computer before diving to get to know it well. This goes for both owning and renting a computer.

You can even take it in the water before starting the dive. Try activating the dive mode, descend a few feet, and see how the information is displayed.

Dive computers won’t require any safety or deco stops if you stay higher than 33 feet (10 m), and you won’t exceed any NDL limit there.

Ascend too fast on purpose to see how the warnings are displayed. Play around with the buttons to see which turns on the backlight and what others do.

Beyond the Basics: Additional Features

Most reputable dive computers will have other dive modes than just open circuit air, like nitrox and trimix.

This requires you to preset the correct dive mode before starting the dive. You must enter your gas data beforehand anyway. But if you require this, then I assume you are well on your way into technical diving, which goes beyond the purpose of this guide.

Air-integrated computers also allow you to pair a transmitter to the computer and display your gas pressure, remaining air time, and other data. In most cases, computer displays don’t automatically show this and must be configured to do so.

Air-integration display on Shearwater Teric

Conclusion: Stay Safe and Informed

Your dive computer is a tool to help you stay safe during a dive and provide ease of mind. But remember its limitations.

It knows nothing about your personal health, physical fitness, experience, susceptibility to decompression stress, etc. You must be the one to consider those things.

It’s also recommended to wear backup gauges, like an SPG and a depth gauge, to be on the safe side.

Otherwise, diving computers are fantastic tools that can take your diving experience to the next level and help you enjoy a lot more. As long as you monitor your depth when descending, stay within the NDL, ascend to 3-6 m, and make a safety stop, you will be fine 🙂

Now you know how to use a dive computer. Happy diving!

Rok Valencic

Rok Vale

I’m a sports enthusiast who enjoys spending as much time underwater as possible. Be that diving, snorkeling, swimming, or just falling off the surfboard. I’m a licensed PADI diver and a licensed fitness instructor. I also have a degree in physics to unnecessarily complicate my life.

FAQ

A dive computer continuously monitors your depth and time underwater and uses a decompression model to determine the NDL (no decompression limit) or required decompression stop depths and times. This is the basic function of any dive computer, although most computers include many additional functions.

The first step in using a dive computer is always to familiarise yourself with it. Read the user manual, see what each button and function does, set the correct units, time, and date, and practice using it.

If your computer fails during a dive for whatever reason, you should immediately stop the dive. Signal your dive buddy that the dive is over and safely resurface.