Dive Computer Working Principles and Main Functions Unpacked

Before you make a decision about buying certain dive computer, let’s answer some common questions about it. In this article you will find basic and general information about these devices and this will help you on the way of choosing the “right one”.
I wrote this article for guys, who are new in diving and know not much about these amazing dive tools that we will tell about below.

We will briefly discuss how dive computer works in following sections

1. Dive Modes & Main Functions
2. Air Integration
3. Dive computer algorithm: liberal vs conservative diving
   
4. Altitude Diving and Personal Conservative Factor settings
5. User Replaceable Battery option
6. Looking after your dive computer

People who have never used before this scuba diving equipment and rely only on Dive Planners and Wheels for multilevel diving ask very often:

• what are they;
• how they operate;
• what is it for me;
• what benefits I will have after buying one;
• why I should invest quite a few hundred bucks in that thing, or maybe I will just continue using my Dive Planner and Wheel...

All of those and other questions are totally justified, so keep reading and you will have all the answers!

Basically, dive computer is a device that shows you depth, temperature, dive time remaining (DTR); no decompression dive time remaining (NDC), and many other things, depending on the model you use, dive mode, and whether you are diving or on surface.

But the main task of it – is to calculate the nitrogen loading and oxygen toxicity levels and compute bottom time and the most optimal and the safest surfacing procedure, manage decompression, and the surface interval between the dives.

All calculations are done in accordance with special mathematical model, named algorithm. In shorter words – dive computer helps us staying out from getting into the Decompression Sickness (DCS) as long as we obey safety rules and computer's warnings and alarms.

Dive Computer Basics: Dive Modes & Main Functions

At the beginning we may mention that all dive computers are produced wit the following mounting options:

1. dive computer consoles (Aeris Atmos ai, Mares Puck Air, Suunto Cobra);
2. dive watch computer (Oceanic OC1, Cressi Archimede 2, Tusa IQ-950 Zen Air);
3. wrist units (Mares Icon HD, UWATEC Galileo SOL, Tusa IQ-850 DC Sapience II );
4. dive computers embedded into scuba masks (Aeris CompuMask HUD, Oceanic DataMask HUD)

Just imagine you are wearing a stylish dive watch computer! At the surface it works exactly as a normal watch, but when you submerge, it switches between “watch” and “dive” modes and starts showing you depth, temperature, dive time, no-decompression time, tissue loading status, air-pressure, and many other information, depending on the model you are wearing and the mode you choose. Sometimes it is even talking to you by producing some beeps!

So, when you go deeper – safe time is decreasing. And if you come very close to exceeding or if you exceeded no-decompression limits (NDLs) – that’s when all those beeps start to irritate you! That moment you may see the nearest decompression stop depth and decompression time are displayed.

Dive computer monitors your nitrogen loading and oxygen toxicity level and may give you a warning or alarm if levels come close to certain maximum allowed.

Also it will definitely give you High PO2 alarm (partial pressure of oxygen) if you reach maximum allowed depth when diving with Nitrox.

And, as well, if your ascent rate is faster than it should be – dive computer will give you “ascent rate warning signal” in order for you to slow your ascent.

Depending on the model of the dive computer, you may have following dive modes:

1. Air (FO2 - 21%);
2. Nitrox (FO2 > 21%);
3. Mixed gas (O% & He% components);
4. Gauge (in this mode it operates as a Depth gauge/Timer without performing nitrogen and oxygen calculations);
5. FREEdive (in this mode dive computer operates as a depth gauge and displays current depth, maximum depth reached during the dive, time in minutes and seconds, gives you depth alarms and dive time alarms, some models may calculate nitrogen and oxygen loading...)

These days, many models may be programmed for up to 3 gas mixes and with possibility of switching between them during a single dive, and dive computers Suunto D9tx and HelO2 by Suunto, may be programmed for up to 8 gas mixes with Helium component.

When you are on the surface, in order to make another dive, you have to calculate residual nitrogen, pressure groups, allowable depths and times by using Recreational Dive Planner.

And dive computer will help you again to perform this task by counting your Desaturation Time and No-Fly Time as well. By using Dive Planner you may easily see all your next dive's depths and times, according to the residual nitrogen and oxygen from previous dives.

Also Dive Simulator (in some models) is available on surface. And this is a very handy addition to all other functions, as it simulates your dive and gives you opportunity to learn dive computer by making 'virtual dive'. You need just enter some basic dive data and computer will calculate depths and times, and will display appropriate warnings and alarms.

On surface dive computer shows you following information & makes functions available:

1. time to Fly (which is a 24 hour countdown timer);
2. time to Desaturate (provides calculated time for tissue desaturation at the sea level, taking into the consideration the personal conservative factor setting);
3. log data & dive history;
4. PC upload/download function

Back to Top

Dive Computer Basics: Air Integration

Next feature – it is the air integration. You will meet hose air-integrated (Aeris Atmos ai, Mares Nemo Air, Suunto Cobra, Oceanic Pro Plus 2, Sherwood Wisdom 2 ) or hoseless dive computers. In this case you need to have a transmitter installed on the regulator (Aeris Epic, Oceanic OC1, Oceanic VT3, Tusa IQ-950 Zen Air, UWATEC Galileo SOL…).

Hoseless models have a Buddy Pressure Check feature, which means that you may check air pressure of your buddy using your own dive computer if your buddy’s transmitter is correctly paired with it.

Dive Computer Basics: Algorithm - Liberal vs Conservative Diving

An algorithm is the mathematical formula that dive computer uses to measure in real time depth, gas mix, time at depth, conservative factor set, altitude, and lots of other factors, and, depending on the algorithm selected,  it calculates for how long diver can stay underwater with a reasonable degree of assurance that he/she won’t get into decompression sickness (DCS).

There are number of different algorithms used in dive computers, each with its own proprietary computations, and its own “liberal” or “conservative” leanings:

1. dive computers that use more-conservative algorithms lessen the risk or likelihood of DCS by limiting dive time (Suunto dive computers);
2. dive computers that use more-liberal algorithms provide the opportunity for longer dive times but, of course, more time spent at depth also increases the risk of DCS (Aeris dive computers, Oceanic dive computers).

So which is best? A younger, physically fit, somewhat-aggressive diver might prefer a more liberal algorithm that maximizes his bottom time, while an older, perhaps not-quite-as-fit diver might want to go more conservative to increase his safety cushion. It really depends on the individual diver’s comfort level. Also diver may select a more conservative algorithm depending on severity of the dive conditions - cold and rough waters, high altitude, this kind of environment.

Dive Computer Basics: Altitude Diving and Personal Conservative Factor

Another important feature is compensation for Altitude diving. Many dive computers automatically compensate for altitude diving and give you adjusted no-decompression times and depths. In some of the models you may set up manually altitude in certain ranges (Suunto and Mares brands come to mind here).

It is worth to mention here Personal Conservative Factor adjustment. Just as an example – if Aeris computers allow us to set this factor just to ON/OFF state, Mares and Suunto models give us possibility to increase or decrease level of conservatism by choosing between highest and lowest levels.

It is usually a great idea to have adjustable levels of personal correction if you dive frequently and in challenging conditions, if you have some health issues or overweight, or if you didn’t dive for a long period of time and returning to diving activities.

Some advanced Suunto dive computers (D6, D6i, D9) allow experienced divers to adjust the level of RGBM attenuation - this function adds more or less conservatism to diving.

Dive Computer Basics: User Replaceable Battery & Data Retention

These day majority of dive computers are made with the diver replaceable battery option, many of them have 'hot swap' option, which means that you need to replace battery within 8 seconds in order to keep nitrogen and oxygen calculations for repetitive diving. And the newest models have data retention, what means that all calculations for repetitive diving will stay in non-volatile memory until new battery is inserted.

When you will be doing research to get the model that is the best for you – go for one, which has ‘diver replaceable battery’ option. It will save you time and money, and also you will be able to continue your diving adventure without any interruptions that may be quite long.

For example, some Mares models (Nemo Excel, Nemo Sport), and Suunto dive computers, like Stinger, D9, D6, D4, and their air-integrated versions must be sent to authorized dealer or local technician in order to change battery. It may not be very convenient, if you dive 3 times a day every day for the period of 10 days, like my mate in Palau!

Some of the models, like Oceanic OC1, Tusa Zen IQ-900, Tusa Zen IQ-950, UWATEC Galileo Luna, UWATEC Galileo SOL and few others have Data Retention function, which means that we may replace the battery at any time between the dives, without losing any nitrogen or oxygen calculations, because all data is stored indefinitely.

Dive Computer Basics: Looking After Your Dive Computer

It is time to say that you have to look after your dive computer. Just follow steps below and you will be all right!

1. you need to protect it from shocks, excessive temperatures, direct sunlight, exposure to chemicals, and do not try to open it for God’s sake to see what’s inside (except times when you replacing the battery)!
2. you may protect the lens as well by placing special protection screen over it;
3. at the end of each day of diving you will need to soak and rinse your dive instrument in fresh water and check the areas around Depth Sensor, buttons and PC interface are clean;
4. to dissolve salt crystals, use warmish water or slightly acidic bath (50% white vinegar and 50% fresh water), and after the bath rinse it with gently running water and towel dry before storing;
5. keep it in cool, dry and protected storage while transporting;
6. it is desirable that your dive computer get inspected every year by an authorized dealer who will perform a factory prescribed function check and inspection for damage and wear

Back to Top