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How to Use a Dive Computer

Ian Fortey by Ian Fortey Updated on August 3, 2021. In

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If you’re just getting into dive computers, there’s a lot to know. They can really take your scuba diving to the next level. But understanding them at first can be a little daunting. And there are a number of different kinds on the market. That makes understanding them difficult. Basically, they all provide the same essential functions. With that in mind, let’s take a look at how to use a dive computer.

What are Dive Computers?

To start with, dive computers and dive watches are the same thing. People tend to use the words interchangeably. The best dive computers can offer up every single piece of info you need to dive safely and successfully. This includes things like:

  • Water temperature
  • Decompression limit
  • Decompression status
  • Current depth
  • Maximum depth
  • Remaining airtime
  • Ascent rate

Most dive computers make use of decompression algorithms and a submersible pressure gauge. These tools help determine your no-stop limit and many other useful things. It offers real time data to make your current dive better.

The no stop limit, also known as no-decompression limit, is a time limit. This is the maximum time you can spend at depth before you need to perform decompression stops. If you exceed this limit, your dive computer can tell you when you need to make a decompression stop. It can also tell you how long you need to spend doing a decompression stop.

This is arguably the most important feature of a dive computer. Decompression sickness is not something any diver wants to experience. If you don’t meet the decompression requirements, you will suffer the consequences. This is serious business.

What is Decompression Sickness?

If you don’t meet your decompression obligation, you will endure some painful consequences. Decompression sickness can be deadly. Decompression stops are required to prevent this. They do so by allowing built up nitrogen gas to leave your tissue.

If you don’t off-gas and let the nitrogen leave through your lungs, there are physical symptoms. These include:

  • Joint pain
  • Dizziness
  • Paralysis
  • Fatigue
  • Loss of consciousness
  • Death

Even when you safely resurface, you are still decompressing. That is why your dive computer will alter your next dive parameters based on the time of your previous dive. Decompression stress is no joking matter.

How to Use a Dive Computer

A good dive computer will have a large enough screen for you to read clearly. The digits should be large and clear as well. Be wary of a computer that is too small. This thing has to be functional or what’s the point. When you’re diving, it displays your important information on screen.

No-Stop Limit: This is the main piece of information to read on your computer. Based on your previous diving, it can calculate your no-stop limit. This takes into account depth and air and so on. It offers data on when you need to take a decompression stop if you passed the no-stop limit. There will also be a countdown to let you know when to start your ascent again.

NDL: Your no-decompression limits or no stop time remaining. This is how much time you can spend at depth without worrying about decompression.

Remaining Air Time: Your planned dive won’t go well if you don’t have dive information relating to air integration, gas consumption, and so on. Your own dive computer can monitor breathing gas levels and the high pressure hose. This is obviously essential for calculating remaining dive time.

Depth: This is a pretty self-explanatory function. It uses a depth gauge to tell you how deep you are. This depth is factored into the algorithms that determine your time limits and so on. This is essential for deep diving.

Time: Losing track of time while diving is very easy to do. Most of us have probably looked at a dive computer and been stunned to see we’ve been down much longer than it seemed. That’s why this is an integral part of the computer. Many dive computers will have an audible alarm to let you know when you’re reaching your time limit. They have various display modes which can cover all of these functions.

Ascent Rate: You need to ascend slow enough that you avoid any physical repercussions. Your dive computer tracks your rate of ascent. If you reach a rate higher than 30 feet/second, an alarm will sound. At that rate, you are ascending too quickly. The ambient pressure is monitored to help you understand this.

Emergency Stop Required: If you do ascend too fast, you need emergency decompression. Your dive computer will alert you to this. It will indicate how long you need to wait for before you can continue your ascent.

Enriched Air Compatible: Your dive computer may be enriched air compatible. If so, it will alter things like your no-stop limit based on whether you use enriched air. Not every diver is aware of how enriched air works, however. In simple terms, enriched air is a more pure kind of air. Normal air is 21% oxygen and 79% nitrogen. However, there are small amounts of other elements present. Enriched air adds 100% oxygen to normal air. That increases the oxygen percentage. That in turn means you can dive longer before you reach your NDL.

Typically an enriched air mix boosts oxygen to 32% or 36%. There are also some blends that get up to 40%.

Dive Info: This is important information to log. Because you still have nitrogen in your blood after a dive, your dive info can monitor this. You can’t do things like flying if you have been on a dive in the last 12 hours. If you have gone on more than one dive, you need 18 hours of rest before flying. Also, if you went diving yesterday, it can affect dive depths and times the next day. All of this is calculated by your dive computer to keep you safe.

Water Temperature: Not every computer includes this, but many do. It doesn’t necessarily affect your ability to dive at all. However, it doesn’t hurt to know how warm or cold the water is.

Battery Power: As with any electronic device, a dive computer is no good without power. The battery warning alerts you if the computer is dying. Always remember to take it on a dive with a full charge.

Compass: An electronic compass may be a little old school but many dive computers do include them. This can be helpful when it comes to getting oriented under the water.

Closed Circuit Rebreather Compatibility: Closed circuit rebreather diving is a kind of diving some divers feel is superior. It’s relatively uncommon still but gaining popularity. It involves supplying pure oxygen and a second gas into a loop. Some dive computers are compatible with this kind of system. A CCR system can greatly alter dive times.

Data Analysis: Most computers work with apps. You can link these to a laptop or smartphone to analyze your dives. You can see where you may need improvement in managing your time, breathing, and so on. Your dive profile can be used to help you dive more efficiently in the future.

What Can’t My Dive Computer Do?

As you can see, this is a great tool. It does a lot. But it can’t do everything. There are some factors that a dive computer cannot take into consideration. Those are all about you. You as an individual are a wild card when it comes to computer calculations. So what does that mean?

Your ability to manage oxygen on a dive is affected by you physically. Typically, the older and heavier you are, the more oxygen you’re going to use on a dive. Weight and age are big factors that can tweak your numbers. A dive computer can learn to compensate for that in time by creating a dive profile. But circumstantial changes may cause issues as well. Let’s say you were feeling sick earlier and are dehydrated now. The way your body processes nitrogen and oxygen will be affected as well. So you need to be aware of yourself, How you feel and your own limitations.

Some dive computers will also have a handful of additional limitations. Let’s take a look at things you want to keep an eye on when picking up a new dive computer.

Depth: One of the big ones you need to be aware of is the depth limitations. Hopefully, any dive computer you find will be good to well beyond your dive depth. Many can handle depths up to 492 feet or more. That should be plenty adequate. But a cheaper quality dive computer may give out far sooner. Always check those final details.

Battery life: In the modern age, this is a constant struggle with nearly every electronic device we have. Your watch, your phone, your laptop. How long do they last on a single charge? Some technology has mastered battery life really well. A good dive computer should offer up a solid 36 hours of battery life, give or take. But we all know from experience that the advertised battery life is sketchy. Compared to what the practical battery life is, it may not be the same. Many times, something that says it lasts for 36 hours means you can only use the most basic functions. So do some comparisons and check reviews to see what real, practical battery life is. Also make sure it’s easy to recharge or comes with a spare battery back if need be.

Memory: If you want to build a good dive profile, your computer needs a memory. This can vary pretty widely from one model to another. Some offer up to 70 hours of memory. Some may be about half of that. The best can get up to 1000 hours. Obviously if you don’t really care about having a profile and analyzing data, it may not matter. But if you are doing multiple dives, it’s good for the computer to have. It can keep track of previous dives. That means it tracks air consumption over repetitive dives and soon. Things like average depth are recorded which can affect subsequent dives. It can continue to give you accurate information based on your dive habits.

Readability: Like we mentioned, a good quality computer is easy to read. But if you look into some off brand dive computers, things get dicey. Be wary of any dive computer with a very small screen. Small screens play well with watches. Some people even prefer a smaller phone. But you want a bigger screen on your dive computer. You don’t know what conditions will be like at depth. The water could be a little murky and reduce your visibility. You need something that is clear and easy to read. If you have to struggle to see numbers clearly, you could be in trouble.

Some designs have an oversized screen. That makes them much easier to read. However, the screen size can be bulky and cumbersome to some. These can be about as large as a smartphone stuck to your arm. It depends on how comfortable you are navigating with such a device.

Cost: You can find dive computers that range from around $100 to close to $1000. Is the $1000 one better than the $100? Honestly, we hope so. But you never know. Compare features to find what you need and what you don’t. Some dive computers come with a lot of frills that maybe you don’t need or want. Others will miss key features. You want to find that middle ground where you get everything you need at a good price. The best computer doesn’t have to be the most expensive. Do you need a computer compatible with closed circuit rebreathers if you don’t use one? If not, don’t pay for it.

Design: Dive computers are typically designed to look like watches. Some can be a lot bulkier than others, though. Some also put a lot more effort into how they look. You can buy them in a variety of cool colors with sleek and sexy looks. If they actually work, then that’s awesome. But remember, you’re wearing this thing underwater. Unless you want to impress sea turtles, the physical appearance shouldn’t matter. Look for function over form whenever you can. It doesn’t have to look lame, but it doesn’t need to look like Kanye West designed it, either.

It’s worth noting not every dive computer looks like a watch. Some are still made in the monitor style. This is essentially like a small probe device that attaches to your suit. You can hold it and read the display. Some divers may prefer this design over the dive watch design.

Durability comes along with design here. Believe it or not, but some of the best computers are still made with less than durable materials. If the screen is susceptible to cracks and scratches, it’s not much good. Likewise, if the band breaks off your wrist, then the dive watch design is pretty pointless. Check reviews if you’re not sure and find out if you’re buying a computer that’s destined to break on you.

Skill Level: Not every dive computer is meant for every diver. Think of them like boats. Everyone can probably handle a canoe, right? But not everyone can handle a 60 foot yacht. There are levels of skill involved in operating them. Depending on where you are as a diver, you need to pick an appropriate diver computer.

Some computers are very clearly meant for beginners. They have basic functions which can help ease you into the idea of using a computer. They’re typically the more affordable options. On the far end of the spectrum are hyper advanced dive computers. These offer a ton of data and features. It can easily overwhelm you if you’re new to using them. Vital info can get lost in all the clutter. Plus, it’s just more than you may need. The price will probably reflect this. No sense spending hundreds of dollars on features you won’t even be using.

Temperature Range: Most dives are done in warm water, but not always. If you live to do cold water diving, you may need to adjust your dive computer. Some dive computers don’t work as well in cold water conditions. But there are some specifically designed to handle a range of temperatures. If you plan on doing cold water diving, make sure you have a computer than can handle it.

How Does a Dive Computer Help with Scuba Diving?

Many new divers want to know why they need a dive computer at all. Well, by now, that should mostly be obvious. It can literally save your life. But beyond that, there are practical applications. You may even consider them the fun benefits of all this data. On its own, a dive computer just provides numbers. A lot of numbers. But you need to know why you should care about those numbers. How a dive computer works makes it a very impressive tool.

Longer Dives: When you learn how to master a computer dive you can enjoy longer dives. You’ll be hard pressed to find any diver who thinks they spend too much time on a dive. All of us wish we could stay down longer to keep enjoying the dive. A dive computer gives you a leg up over traditional dive tables. That’s because the computer works in real time. A table is based on static information.

We’ll look at dive tables in more detail in a bit. But for now, know it’s a chart that explains depths and times. You look at depth and determine your dive time. It’s straightforward once you get the hang of it. But it is also flawed. For instance, what if you go deeper for five minutes? What if you don’t stay at that depth the whole time? That will affect your numbers, but the dive table can’t account for that. In real time, your computer can. It will make adjustments based on depths and your breathing.

With the real time monitoring of conditions, a dive computer will be able to add several minutes. That’s in comparison to results from a dive table. Considering you’re probably investing a lot of time and money in your dive, those minutes count. You want to make the most of them.

If you are diving with enriched air, the numbers are even more impressive. The computer can do the calculations for you. It can determine oxygen percentages and depths. This is stuff you know already as a diver, but most of us forget in the moment. The calculations can definitely get away from us based on ascent rates and more. The computer takes the stress out and makes it all easier.

Informed Dives: The dive profile we talked about can really be useful for future dives. If you dive in the same areas or at the same depths, you can start analyzing data. Over time, you’ll come to understand your own oxygen consumption. You can also see how it can potentially improve as you keep diving. As with anything, practice makes perfect. The more you scuba dive, the better you get. The better you get, the longer you can do it. That goes to our above point.

The computer is able to compare this data for you. You can see how you improve over time and become a better diver overall. It also helps you adjust your expectations for each future dive.

Safer Diving: The big benefit to a dive computer after all the fun is the safety factor. Human error has led to more than one case of decompression sickness. The computer is far less prone to making errors in calculation. It doesn’t lose track of time. It doesn’t ascend too fast without realizing. It doesn’t forget or overlook anything. A dive computer can save lives.

Dive computer fails are rare. Certainly less common than issues with human errors. If you buy a good quality model, dive computer fails are not the sort of thing you probably won’t need to worry about.

If you are concerned about a dive computer going wrong, play the odds. You should always be diving with someone else. If you are both wearing one, odds are at least one is working correctly. All things being equal, there are far more reasons to trust how dive computers work than not.

Necessity: If you are a frequent diver, you have seen this in action. When you head out on dives with guides, they expect you to have a dive computer more often than not. For some basic dives this may not be the case. Beginner divers can usually get away without. But the more advanced the dive, the more important a dive computer becomes. And, as an advanced diver, you’re more able to appreciate this.

If you’re new to diving, this is a good thing to remember. If you’re planning a vacation soon and you want to dive, look into it. Ask if a dive computer is required for any dives you have booked. Sometimes operators forget to mention it.

If you’re serious about diving, you’re going to want to buy one. Now that can be a steep investment. A top of the line dive computer can set you back hundreds of dollars. But there are also good quality dive computers that cost much less. You can get a good, reliable unit that won’t break the bank.

Again, a casual diver maybe won’t need to invest in a computer. If you only do some shallow diving, or once every few years, then that’s fine. But if you plan to make a hobby of it, buy a dive computer. You’ll find it to be nearly as essential as some good fins and a mask.

What are Dive Tables?

If you’re an old school diver, you remember dive tables. People still use them but not nearly as often. The dive computer has successfully replaced dive tables for most of us. The reason being that a dive computer is just a faster and more convenient way. It’s the difference between doing math long hand on paper, or using a calculator. You can get the same information but in a different way. Dive computers are faster and more convenient. And unlike a dive table, you can bring it with you.

A typical dive table comes in a booklet or card form. It’s basically just a reference item. It provides the crucial info you want before actually hitting the water.

Dive tables detail dive data like:

  • How long you can stay at a specific depth
  • The time it takes to get to the bottom, stay there, and resurface known as “bottom time”
  • How long before you should resurface
  • How deep you can go with the air you have
  • Safety stop times
  • Decompression limits
  • Nitrogen levels
  • How long you should wait before diving again

For many new scuba divers, dive tables are very hard to understand. The information looks complicated and overwhelming. However, once you have learned how to use dive tables, they are pretty straightforward. That said, many divers prefer a personal dive computer. Most dive computers offer the same info as dive tables plus much more.

Because a dive table offers static data, it is not as versatile as a dive computer. But it’s good to understand how both work. One of the big problems with dive computers is how they’re understood. Many divers don’t fully understand why it provides the information it does. It’s important to know the science behind the data presented.

Any diver should have completed dive classes. These explain the numbers behind ascent rates and dive limits. It can be easy to get a little lazy and forget over time, though. Again, just like a calculator or spell check, we tend to rely on technology too much. You may be tempted to let the dive computer do all the work without questioning why or what it does. That’s fine when it comes to letting a calculator do long division for you. But a dive computer can affect your health. For that reason, it’s best to know exactly what it’s doing and how.

We recommend reading the manual that comes with your dive computer fully. Learn all the features and how to use them. And make sure you brush up on your dive knowledge as well. You need to understand these fundamentals if you want to be a safe and successful diver. We never want to see anyone get hurt out there.

The Bottom Line

A dive computer is an extremely helpful tool. We consider it essential dive gear. You have your mask, your fins, and your computer. It makes sense to have one if you have any interest in making scuba diving a serious hobby. The benefits to using one can’t really be overstated. It’s like GPS for your car, or Google on your computer. If it makes a job easier, why not take advantage of it.

The key thing to remember is that you should understand how and why it is giving you the data it is. Understanding the information ensures better dives and safer dives. As always, keep safe and have fun in the water.

About Ian

My grandfather first took me fishing when I was too young to actually hold up a rod on my own. As an avid camper, hiker, and nature enthusiast I'm always looking for a new adventure.

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