Guide to Dive Computers

Guide to Dive Computers

Dive Computer Guide

What is a dive computer? A dive computer or personal decompression dive computer is one of the most critical pieces of equipment and divers safety device.

As a primary function, all decompression dive computers measure time and depth and give you the best possible ascent rate to the surface using a pre-programmed algorithm and thus significantly reducing the chance of getting decompression sickness.

The Dive Computer is now an essential piece of a scuba diving kit; it will allow you to stay underwater longer and dive safer. It is most likely one of the first items a novice diver will buy after completion of their open water course. Our online store offers a broad selection of dive computers, and they differ from each other in shape, type of display, power supply, dive algorithms and dive functions.

Someone once said "Tell me the mission, and I will tell you the tools you need to complete it". Mike's Dive Store has always been about offering the right diving equipment for the type of diving our customers enjoy, and the first question our staff will ask you at our Chiswick store is: "What sort of diving do you do?"

Beginners Dive Computers

Are you an open water diver, who enjoys regular recreational dives? Then the entry-level dive computer may be for you.

A considerable advantage of an entry-level computer is that it will not break your bank account. Still, it will be a quality instrument that shows all the necessary information making diving more enjoyable. 


So let us have a look at the design and display first. A budget computer typically features a "hockey puck" shape module with a smaller segment monochrome LCD screen that shows all your essential dive information and a user-friendly interface with two, three or four buttons for menu selection and navigation. Dive computers with slightly higher price tags from companies like Suunto offer a dot-matrix display with fluorescent display as well as a backlight which makes reading data during low visibility or night diving much easier.


What about all the functions? Nowadays, even an entry-level, well-priced dive computer packs an impressive amount of features and come with air and nitrox functions as standard, so you can choose between diving on air or nitrox. Entry-level models will usually allow a selection between gauge only, freediving and scuba modes for divers who have a multi-disciplinary approach to the sport. 


Modern dive computers come with audible and visual warnings as standard. They alert the diver to reaching no-deco limits, maximum depth or maximum time - a handy safety feature for newbie scuba divers. Another built-in safety feature in scuba diving computer is RNT (Residual Nitrogen Time) and No-Fly advisory. From your Open Water Course, you already know it is easy to track nitrogen loading for a single dive, but it becomes a bit trickier for multiple dives.

A dive computer tracks your nitrogen absorption over multiple dives and calculates nitrogen saturation for you. At the same time, the NO-FLY icon advises the time you should avoid air travel. Last but not least, entry-level dive computers will have altitude diving adjustment. This feature comes in handy when you are diving at altitude and have user changeable or automatic adjustment for different altitude ranges, ensuring the algorithm properly matches your saturation and desaturation rates.

Dive Planner and Log

One of the immensely useful functions in a dive computer is the ability to plan and log your dives. Selected dive computers will have a built-in dive planner so you can have a look at a live simulation of your dive, which is quite an improvement over your RDP. It is also good fun to be able to flick through the log and see where your diving career took you over all the years and how diving profiles have been improving with your career progression. A Dive Log is a good way of gathering data and useful dive information like the type of suit used; diving conditions and marine life that you encounter. 


Now, more than ever, there is a growing competition between dive computers manufacturers resulting in more features like PC/Mac connectivity included even in the entry-level computer. Most dive units will connect via the dedicated cable supplied with your dive computer or sold as an optional feature. Most of the manufacturers offer dedicated software or even mobile applications that you can use alongside your device wherever you go. It can also be a fantastic back-up tool if you prefer to log your dives in your traditional paper logbook. 

Power Supply

In terms of battery type, entry-level computers have either user-changeable battery or a sealed battery compartment that can only be opened by a trained and qualified technician. The difference between the two is that while you can change the battery yourself with the first option, the latter lasts longer but requires sending your computer to an authorised dealer. Our Mike's Dive Store in Chiswick runs a Dive Computer Service Centre and can even change batteries in selected models while you wait to make sure your equipment is ready for your next diving adventure at short notice.   

Looking at what is available on the market today, a beginners dive computer costs from £230 up, which is a great bargain considering it is a divers safety device that performs quite complex calculations throughout the dive.


Suunto Dive Computers | Scubapro Dive Computers | Shearwater Dive Computers |  Aqualung Dive Computers | Mares Dive Computers | Garmin Dive Computers

Advanced Dive Computers

Are you looking to expand your diving skills in the future, try more advanced diving using multiple nitrox gases and multiple tanks? An advanced dive computer may be for you.

With regards to dive computers, 'advanced' can have two meanings. Firstly, in terms of newer technology and the extra features that it allows and secondly, in terms on function for deeper or longer diving that additional training and skills allow.

Significant improvements from beginners dive computers are the size and type of display and selected function. Advanced dive computers feature dot matrix screens in cheaper versions while more expensive computers will be equipped with a large, full-colour display. Full-colour screen means better, more understandable information projection and more user-friendly operations. Colour coding gives you fantastic readability - most computers use a traffic light colour system with green or white for all-is-good, the amber colour is to attract your attention while red means you are exceeding your planned dive parameters. 


Most of all advanced dive computers should possess gas switching capabilities and calculate decompression with a different air, and nitrox mixes for more advanced, deep air and extended range diving. 

As you dive with higher oxygen content gases, your advanced computer should give you the option to choose oxygen partial pressure and calculate your CNS (oxygen loading) and OTU (Oxygen Tolerance Unit). PPO2 setting will allow you to set up correct partial pressure for your bottom gas mix and your decompression gas. Central Nervous System (CNS) Oxygen Toxicity is a measure of how long you have been subjected to an elevated partial pressure of oxygen and shows on your dive computer as a percentage of maximum allowance. 

One other function introduced at this level is a digital dive compass. Having a compass built into your dive computer means that there is no need for a dedicated stand-alone analogue compass. Better dive computers will have a multi-axis, 3D tilt-compensated digital compasses, which can be comfortably read in different positions and does not have to be placed horizontally for accurate readout. 


There is a meaningful improvement in the safety features of advanced dive computers. Apart from audio-visual alarms, selected advanced dive computers hold a handy feature like a vibration alarm. Your unit will alert you with a vibration if you are exceeding your dive plan or dive parameters are outside the expected values. 

Air Integration

Besides, at this level and price of £400 and above, a lot of advanced dive computers offer air integration with optional wireless transmitters which can handle reading from one or multiple tanks. Gas integration helps with gas management by taking pressure readings from your tanks and calculating how much longer you can stay underwater at a given depth. It will also take into consideration your breathing rate and adjust your decompression accordingly. 


One of the latest developments in dive computer technology is Bluetooth connectivity - it enables transferring data from your computer to your PC/Mac or Mobile without the need for an additional cable. This option is standard not only in advanced dive computers but slowly finding its way into entry-level units too. 

Power Supply

Apart from user-replaceable and sealed batteries, advanced dive computers often feature rechargeable batteries. It is, of course, a matter of personal preference but having a rechargeable battery means you don't have to worry about a spare battery when you need to change it in the middle of your diving holiday. A rechargeable battery may last you a shorter time, but you can charge it from multiple sources such as mains  USB adapters, laptop USB ports or even in some cases from a power bank.  


Suunto Dive Computers | Scubapro Dive Computers | Shearwater Dive Computers |  Aqualung Dive Computers | Mares Dive Computers | Garmin Dive Computers

Technical Dive Computers

Are you an advanced diver who is thinking about going the technical diving route?  A technical diving computer is the way forward!

The selection of technical dive computers has grown immensely over the last decade, and they present the latest technology in the diving industry. Technical computers will undoubtably feature some advanced options but that doesn't mean you can use it. A technical dive computer will function just as well for a beginner as it will for an experienced tri-mix diver.

Design and Screen

Technical diving computers are presented mostly, with one or two exceptions, as a stand-alone wrist-mounted piece of equipment. An excellent technical diving computer now-a-days is a complex machine but with a smooth, user-friendly and intuitive interface that will allow tracking dive profiles on an open and closed circuit dives. Modern technical diving computers feature almost exclusively dot matrix and colours screens for best readability and information display. Better models offer highly customisable display which means you can decide which extra features will be displayed on your screen.  


A technical diving computer has to have the right level of customisation which means its software enables the user to choose different breathing gases like air, nitrox up to 100% and trimix. The technical diving computer will share a lot of feature of a well designed advanced dive computer like air integration, full oxygen tracking, multi-axis tilt-compensated digital compass, O2 partial pressure settings. 

The most significant improvement from advanced dive computer is user-selectable dive mode which allows choosing between open circuit diving as well as closed circuit. The closed circuit options accommodate the growing number of recreational and technical rebreather divers. Some units like Shearwater will offer options to plug into the rebreather electronics for oxygen sensor reading.  

Another development in dive computer technology resulted in dive gear manufactures like Scubapro introducing "Human Factor Diving". This unique feature enables the computer to read your heart rate and body temperature and factor it in your decompression calculations.

Power Supply and Connectivity

There is a clear trend for more advanced and technical dive computers to have a user-changeable or rechargeable batteries and sealed type batteries are only used in a small proportion of watch style computers. Likewise, Bluetooth connectivity seems to be the latest preferable option in top-spec technical diving computers connecting the user with cloud services. 


A technical dive computers for advanced mixed gas diving bears a price tag in excess £600. Price may seem high, but we think the number of features and the quality of technical dive computers are worth the price, primarily if they will serve you well for years to come. 


Suunto Dive Computers | Scubapro Dive Computers | Shearwater Dive Computers |  Aqualung Dive Computers | Mares Dive Computers | Garmin Dive Computers

Dive Computers By Style

What style of dive computer do you prefer? Since the release of the Uwatec Aladin a couple of decades ago, the dive computer has evolved into different styles and reduced in size considerably. There are three main types of dive computers available on the market: wrist-mounted dive computers, wristwatch style dive computer and console dive computers, with each style having advantages for its users. 

Wristwatch style computer. A decade ago all the wrist computers were quite large but as technology advanced and became smaller, so has the size of dive computers. The massive advantage of a watch dive computer is that you have just one device which is packed full of features in something very similar to a regular size wristwatch.

This type of dive computer appeals to numerous warm water divers because of its low profile and ability to be worn every day. Quite a few divers will tell you; it's also about the lifestyle, practicality, functionality and fashion - it looks cool. If you wear it on your wrist all the time - it is unlikely you will forget it on your dive trip, plus it will wake you up with an alarm for your first dive at 05:00 on your dream liveaboard holiday.

Wristwatch style computers from most diving manufacturers feature multiple dive modes like gauge only, apnea or freediving mode and full scuba mode. Air integration via a transmitter and smartphone or Bluetooth connectivity and colourful display are features of the selected models. A digital compass is one of the most significant features in a good wristwatch style dive computer, and selected models offer them as standard. The top diving watches from Suunto or Shearwater offer air, nitrox and trimix with gas integration for multiple tanks. Fantastic AMOLED display from companies like Shearwater is a treat to user eyesight, and with their ultra-sharp screen, it is considered by many as the best wristwatch style dive computer. 

Smart Dive Watch. The latest development in watch type diving computers from manufacturers like Garmin, which introduced the Garmin Descent Mk1. Smart Dive Watched spoils user with functions like three-axis digital compass, gyroscope and barometric altimeter, GPS, heart rate monitors and better smart phone integration and will appeal to someone with an adventurous lifestyle.  

Wrist-mounted dive computers - The wrist mounted dive computer is a more traditional type of dive computer which rules over dive watches mostly with the size of the screen. Larger wrist-mounted dive computers are more appealing to divers who prefer bigger screens, dive in waters with decreased visibility or don't want to wear a watch. A larger screen means its more comfortable to read, with all the information being displayed in big digits and clear sections on the screen, hence they are the number one choice for many advanced, cave and technical divers. Another advantage of traditional wrist-mounted dive computers is the size of buttons, which can be operated in a thick drysuit or neoprene gloves, they are preferred among divers enjoying cold water diving. Wrist-mounted dive computers tend to have longer straps, so they fit over drysuits better then watches but the downside of a large wrist mounted dive computer for some is that it's a dedicated stand-alone piece of equipment that will be worn during the dives only. 

Console Dive Computer is a dive computer that offers most of the features of a wrist-mounted one. Still, the main advantage of a console dive computer is that it is attached to your regulator rig, creating a neat and tidy package. Predominantly they will also have large screens with large push buttons for more natural operation. Dive computer consoles come with different features, but better ones will offer air integration via the hose which means it will show you how much air you have in your tanks and will take your gas consumption rate to calculate how much time you have left at any given depth. Another typical function in a diving computer console is an analogue or digital compass. Scubapro, Suunto and Oceanic are prime examples of well-designed and functional dive computer consoles with electronic style compasses. 


Suunto Dive Computers | Scubapro Dive Computers | Shearwater Dive Computers |  Aqualung Dive Computers | Mares Dive Computers | Garmin Dive Computers

Some may argue that the downside of a diving computer console is you need to reach for it, each time you need a piece of information from your computer. Going for your console reading can be a bit tricky when you have increased task loading, like making videos or taking photos or doing decompression stops. Some also argue that another slight disadvantage of a console is that it is prone to knocks and being damaged more than a wrist computer. It sits low, and if the diver is not careful, it will end up under the tank or dragging over a reef. 

Terminology and Jargon Busting

Diving Algorithm - a set of mathematical formulas that take into consideration variable real-time data like pressure, time, breathing gas, water temperature to calculate the safe diving limit 

Algorithms by manufacturer: 

Suunto - RGBM

Aqualung  - Pelagic Z

Atomic - Recreational RGBM

Oceanic - Dual Algorithm - Pelagic Z+ (ZHL-16C) and Pelagic DSAT

Shearwater - Bühlmann ZHL-16C with optional VPM-B and VPM-B/GFS

ScubaPro - ZHL8 ADT MB

Cressi - Haldane/RGBM

Mares - RGBM or Bühlmann ZHL-16C

Garmin - Bühlmann ZHL-16C 

Suunto - RGBM

Segment display - a simple digital display divided into sections that show all the numerical information, but is limited in showing word information.

Dot-matrix display - an improvement over segment display where dive computer can project word information onto the screen. 

LCD display - liquid crystal display. It is usually featured in the top dive computers - offers excellent resolution and colour to convey necessary information better. 

Dive modes - computers software offering different modes to suits different types of diving like gauge only, apnea/freediving Mode, air mode, nitrox mode, trimix mode, open-circuit mode and closed-circuit mode. 

LED Backlight - light-emitting diode screen which lits up when needed - particularly useful function during night dives.

RNT Residual Nitrogen Time - used to calculate nitrogen in your body during multiple dives

Bluetooth Connectivity - a wireless connection of your dive computer to PC/Mac or a smartphone. 

PC/Mac integration -  dive computer enabled to connect to a PC/Mac via a dedicated cable

Air integration - a way of reading cylinder pressure by attaching a dedicated transmitter to the regulator 1st stage. 

Altitude Adjustment - a feature in dive computers allowing user-changeable or auto adjustable setting for altitude diving

Digital compass - computers equipped with a digital compass where azimuth is being displayed on the screen. Better models have tilt compensation or are 3-axis enabled, which means you do not have a perfect horizontal alignment for correct readout.

CNS/OTU Oxygen loading - Central Nervous System Oxygen Toxicity is a measure of how long you have been subjected to an elevated partial pressure of oxygen and shows on your dive computer as a percentage of maximum allowance.