Does Not Compute - The scuba dive computer

This is my computer. There are many like it but this one is mine. My computer is my best friend. It is my life. I must master it as I must master my life. Without me, my computer is useless. Without my computer I am useless. I must use my computer true. Before God I swear this creed: my computer and myself are defenders of my dive, we are the masters of the sea, we are the saviours of my life.


Computers are running the world. I am firmly convinced somewhere along the line everyone works alongside a computer and ultimately works for Google. Mobile phones are practically computers now; even TV’s are doing things that 10 years ago a computer couldn’t handle. Scuba diving is no different; you can’t dive without a computer.

Or can you?

Not really.

At the present moment in time I am trying my hardest to buy myself a new dive computer. In a vain attempt to purchase my new fangled gadget I am even selling my beloved WALKMAN (click here to bid!!), initially purchased in 1989.

Needless to say this attempt at raising capital is failing miserably. However, I shall not be deterred and will relist with an additional sweetener if needs be, perhaps Michael Jacksons other silver glove?

There are a ton of computers on the market; far too many to list, but there are certain types to choose from. Here is what I had to consider:


This is the bog standard, as simple as it gets computer. Some divers will argue;

It’s not a computer; it’s a bottom timer!

Indeed; I think they merely need to relax a little.

What does it do?

  • Depth
  • Time
  • Log
  • Temp 

Remarkably the market is very small for these units. The only 2 real options are:

  • Uwatec Bottom Timer: cheap, simple, effectively disposable, but last for about 10 years. 
  • Liquivision Xen: Hideously expensive, amazing display, excellent timer functionality. 

Who wants one?

  • Recreational divers that know how to use NDL tables efficiently. 
  • Technical divers have them as a back up to be used alongside tables in case of primary mixed gas computer failure. 
  • GUE trained divers use them as a primary gauge as they calculate decompression stops manually. 


These bad boys are the meat and potatoes of the computer market. The definitive dive computer some would say; some being me.

What does it do?

  • Depth
  • Time
  • Log
  • Temp
  • Nitrox (up to 50%)
  • Decompression info
  • Dive planning feature 

These are magnificent tools of the trade. These computers are great for just keeping a watchful eye on you when you’re scuba diving.

They offer the same tools as the bottom timer plus a few more tricks.

The main addition is the decompression and nitrox stuff. When diving, the computer will countdown the non-decompression time remaining. Of course we all learned our PADI tables initially, but I challenge any regular scuba diver to accurately tell me the NDL at 28m. (all answers in the comments section please!)

The NDL clock is a valuable tool in preventing a diver from inadvertently entering a decompression obligation without correct planning; and to get the most bottom time on a dive.

Most of these models will also track CNS loading when using nitrox, your surface interval (adjusting NDL accordingly on repetitive dives) and no-fly time; all really great for keeping a diver safe.

You can set these computers to use nitrox up to 50% which is perfect for most diving.

I find this type of computer very useful when on holiday, especially for repetitive diving or liveaboards.

There are hundreds of computers on the market that do the job; it really is personal preference of which additional features you would like.

Personally I would buy one that has a “gauge mode” function as this will allow it to be used as a backup bottom timer should your diving progress into the technical realm.

Who Wants One?

  • Recreational scuba divers. 


The multiple gas computer pretty much does what is says on the tin, and is the next step up from recreational computers; used predominantly when a diver goes ‘techie.’

What does it do?

  • Depth
  • Time
  • Log
  • Temp
  • 2/3 programmable nitrox mixes up to 100%
  • Decompression info
  • Time to surface (most do this taking into account the programmed gases)
  • Dive planning based on programmed gases 

In short is does everything a recreational computer and bottom timer does but with the addition of being able to program a second nitrox mix into the thing.

This is useful if you are conducting a decompression dive. You can set mix 1 to be your backgas, 21%; then set a second decompression gas, 50%. Upon reaching the decompression stage of the dive you switch gases, tell the computer you have done so, and it cleverly recalculates the decompression obligation.

There are a number of 2/3 gas computers on the market. The Uwatec Tec 2G, Apeks Quantum or Suunto Vyper 2 appear to be the most popular.

Who Wants One?

  • Divers that carry an additional cylinder/s with a different mix on dives.
  • Advanced nitrox divers


These are the daddies of the computer world. There are far too many features to even begin to list, but they include:

  • Depth
  • Time
  • Log
  • Temp
  • Multiple programmable gases (some do up to 10 gases)
  • Trimix enabled
  • Decompression info
  • Time to surface (most do this taking into account the programmed gases)
  • Dive planning based on programmed gases 

Some of these computers are also compatible with rebreathers; being hardwired into the unit.

The market for this type of computer was initially dominated by, the now iconic, VR3. Over the last few years however, competition has been increasing and the majority of manufacturers are producing top end pieces of kit.

The old VR3’s are now used to keep doors open.

The top contenders are VR, Liquivision, OSTC and Shearwater. Some are rebreather friendly, which is reflected by price, but they are all pretty much amazing. The common deciding factor on such units comes down to display and battery life.

Many divers that use these machines have a preference for specific decompression algorithms, which may also determine which computer to buy.

Who Wants One?

  • Technical open circuit and rebreather divers. 


Some computers do other things which may appeal to certain types of diver.

  • Air intergration: This includes a remote sensor that is screwed into the 1st stage. Information on gas usage, sac rate, time left in tank, is fed to the computer wirelessly. Multiple sensors can be used allowing a diver to also keep track of a buddy’s gas. 
  • HUD: Oceanic do a computer which sends information to a heads up display in the divers mask. 
  • HP gauge computers: Some console computers are integrated directly to the high pressure hose, giving similar information to the remote sensors.
  • Download: Nearly all computers allow the downloading of data onto a desktop or laptop computer. Bear in mind that often the hardware required isn’t included with the unit itself, and can be expensive when purchased on its own. 


Herein lies the reason I haven’t slept for weeks, consistently trawl internet forums, and have read every dive computer review ever put to paper; or screen.

Which bloody computer do I want? 

That’s easy; I WANT an OSTC 2n. It’s amazing, has the best display ever, and; on the list of the best things I’ve ever seen comes second; ... beaten only by the pyramids.

At £650 however, it’s rather expensive. Factor in that my oil fired boiler has recently decided to stop making my house warm on the run up to winter; I probably won’t be getting one anytime soon.

Neither will Wifebuddy.

I know which one I want, the real question is…do I need one?


Currently I have a Mares Puck; a basic no nonsense recreational computer, that can also function as a bottom timer. It suits my recreational diving as it can do all the things I have talked about, and when set as a gauge, it can be used for my technical diving along with the aid of decompression tables.

In short I don’t need a computer; I already have one that does everything.

Carlsberg don’t make computers…

Go buy a Mares Puck.


  1. Brilliant!! Buying a dive computer is a big investment but it is oh so personal as well.
    Bloody bummer about the boiler. Hope Santa puts you on the nice list this year!

  2. Thanks Tara!

    I think, as with most scuba gear, you have to know where your diving is heading when you buy a computer.

    Problem is you never know where scuba will take you when you start!

    Fingers crossed for Santa...

  3. Excellent again dude!
    I have a Puck too. Maybe you can answer a question? When i look at my log book(in the computer), some dives have the DECO icon (when i did do a little deco), and some have DECO plus the arrow under the word. Can't find what it means! I missed a deepstop maybe?

  4. Another thing i find about the puck: on repetitive dives, it tends to want to put me in deco A LOT faster than my buddies computers, as if it didn't calculate the same surface interval time...annoying!
    (and i didn't program a personal factor).
    Do you also have that problem? Otherwise i kinda like my little puck! Specially that i did not need to mortgage my house to buy it...

  5. Hi Jean Louis,

    I checked my PUCK and all my deco dives just have DECO on the screen, but no arrow. The arrow, as i'm sure you know, signifies a STOP. Maybe it stayed on if you left a stop a little early?

    I don't think it's anything to do with deepstop, as it actually displays the text DEEPSTOP along with the depth when required.

    I must admit i do find the PUCK very conservative. I'm always a minute or two into deco before Wifebuddy.

    The PUCK uses RGBM Mares-Wienke Algorithm, which is a bubble model, for decompression. If your buddy is using a different computer it's probably just running a more aggressive deco profile.

    At the end of the day it's a recreational computer. If you are constantly running decompression dives you may want to use a computer that allows you to run a different algorithm.

    Look on the bright side; you're safer! :)

  6. Knowing what you want your computer to do is handy Andy. hah! I rhymed ....
    anywhooo .. I had a Mares Nemo for years and I loved it., Til I starting slinging a stage with a different gas mix. Then I had to upgrade. And take in to account what I was going to do next.
    Poor old Nemo - she karked it recently.
    Bent her silly. She wont even turn on for me now.

    She would be in deco 2-5 minutes before my Suunto Vyper would.
    For the majority of recreational divers, I'd say that level of conservatism is good.

  7. Kerri has the nemo, it's a lovely wee unit; just a shame it doesn't have a gauge mode - would be a super back up for the tech stuff. Weird the way Mares decided to leave it off?

    I agree, for recreational diving the more conservative the better.

    I used a Suunto doing my tech course in Malta, nice computer. I found it quite conservative as well. Again, no bad thing - decompression is not an exact science!

  8. I prefer SW is simple to use very user friendly the problem with OSTC is that it is bigger and got more weight, with SW has 5 Ccr gases and 5 OC gases i can organize easily it has bigger screen that the OSTC and the screen can flip left to right.

  9. Yup, the SW is a nice unit for sure!

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Thanks for commenting, I appreciate it!

Safe diving buddy.