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The Apeks Quantum Dive Computer October 4, 2008

Posted by Chris Sullivan in Equipment.
Tags: , , , , , , ,

The Apeks Quantum was my first computer, purchased in November of 2005 just before a trip to the Turks and Caicos. It is Nitrox-capable, accommodating 2 gas mixes. The first gas can range from 21 to 50% Oxygen, while the second (decompression) gas can go all the way to 99%. Other settings include various alarm thresholds, the date and time, and metric vs. imperial. It’s a good idea to commit the method of switching from metric to imperial if you ever have to reset the computer. Put it in Dive Mode and hold both the “A” and “B” buttons down for 5 seconds or more. It logs in 15 or 30 second increments, allowing you to trade off the detail against the number of dives it can record. It also can act as just a bottom timer.

After more than two years of diving with this computer, including some modest (no more than 15 minutes total) decompression diving, I bought a second one as a backup so I could feel more confident on technical dives. The most extreme dives I’ve used them on were a 30 minute drift dive ranging from 160 to 175 feet and 2 hours of bottom time inside the wreck of the Daryaw at about 85 feet. The latter dive required almost an hour of deco on my back gas which was a 35% mix. I used 80% for the deco mix on the drift dive for a total of about 30 minutes, as I recall.

Other team members on both dives were using Cochran Computers, which demand far less decompression time. On the one hand I feel bad when the other divers are waiting around for my computer to clear, but on the other I appreciate the extra safety built into the longer schedule. These same divers are encouraging me to get a Cochran but I could buy half a dozen Quanta for the same price. I’m considering taking a Trimix course at some point, though, so if I want to use a computer rather than tables I’ll be stuck shelling out for something with that capability.

Pair of Apeks Quanta - the one on the left doesn't work

Pair of Apeks Quanta - the one on the left doesn

Unfortunately I have had problems with the older unit (which is out of warranty). I had left it in the drawer for a week and then found it with a blank screen. Of course, the first thing I did was change the battery, a standard CR2032, which had depleted from 3V to about half a volt. However, the replacement didn’t work. A couple of days later the screen came alive but the computer still malfunctioned. Based on the behaviour of the unit I believe that the large central “Mode” button is locked in the pressed position. I’d like to take it apart to see if there is mechanical damage (there was some grit in the battery O-ring cavity and obvious moisture behind the glass) that can be repaired, but the back is fastened by very small diameter Torx screws and I’ve yet to locate a suitable tool for it.

I’m not the only one who has had problems. Others have reported that after 100-150 dives, either the screen dies or the depth sensor fails. The Cochran on the other hand has a reputation of being rock-solid. The one feature that turns me off about Cochran is the lack of manual gas switch. On the Cochran you program in the depth that you switch to a deco gas and the computer automatically switches when you ascend to that depth. I don’t know how you’d do an air break with that, or handle a failure that prevents you from breathing the intended deco gas for a few minutes or more. The only way to switch the Quantum is to hold the “A” button down for 5 seconds.

Aside from the failure I’m very happy with what the Quantum does. The consistency between the 3 units I’ve tried has been impressive in both depth accuracy (all within about 8”) and decompression times (all within a minute). It’s easy to use and easy to read under water, and has never let me down on a dive.

On the Labour Day long weekend I borrowed a friend’s unit to use as a backup and took it tech diving. He has the computer interface and the software produced some very cool charts of my dives. He was half-hoping I’d break it as it was about to go out of warranty, but it worked just fine. I’m not sure I’ll ever buy another one of Quantum because of the reliability issues, but functionally it’s been a good computer at my level of diving. I do recommend carefully cleaning (or even better replacing) the battery compartment O-ring from time to time.



1. Moe - October 4, 2008

Thank you for the valuable information.


2. deepstop - October 4, 2008

For some reason the caption on the picture was incomplete. It should say “the one on the left doesn’t work”.

Thanks for your comment Moe. I’m glad you found the information useful. I’ll have some more information on it in a couple of days.


3. Moe - October 5, 2008

About the picture is all right. I went snorkeling the other day with my friends and since then I got obsessed about diving I really want to learn how to dive. I guess I will soon become PADI Open Water diver. But I am busy with college at the moment. But between now and then I will just read stuff in Wikipedia and watch Videos in Youtube 😉

I just want to say thank you for the effort that you put in this blog, I have read most of entries you put previously. The way to you explain the tech information is simple even for me.


4. The Apeks Quantum Dive Computer, Part Two « Chronicle of an older diver - October 6, 2008

[…] Apeks Quantum Dive Computer, Part Two Part 1 of this topic, posted on Saturday, described this computer, its features and benefits, and how one of the two models I owned suddenly […]


5. deepstop - October 12, 2008

Part 2 and Part 3 of this post are elsewhere in this blog.


6. Mark Smith - February 16, 2009

I have the same comp (Quantum) 3 yrs. / 257 dives. Also I am an Assistant Instructor. while on a wall dive (Willis for any Victoria B.C. divers) my comp. started flashing that I was red octobering and then I was 300 ft. then red octobering then deco deco deco red october blank I had just had the battery changed. the o-ring was cleaned lubed maybe 3 dives on the new battery. I have never bumped dragged dropped or abused my gear. I left my wife for my dive career. I truly like the quantum but that is the only thing that has ever jarred me under water…….maybe suunto…..


deepstop - February 18, 2009

On my first dive today here in Cozumel I looked at my computer after a minute underwater and found it was in Gauge Mode. Strange. Don’t know how it got there. Maybe I bumped it in the right sequence (Mode button, then Button B) but it seems unlikely. I continued the dive taking a long safety stop and then reset it with and did the second dive with the safety factor set to one, and did another long safety stop. I hope it doesn’t happen again.

I have a Shearwater Pursuit (made in Vancouver) on order. I expect it will be a lot tougher.


7. Diving the Oriskany - Day 2 « Chronicle of an older diver - April 24, 2009

[…] the day before, but in the evening one of them stopped working completely, in a very similar way to one of the ones I used to have. It was the older of the two (like mine) and continues the pattern of these computers having a […]


8. Wreck Training on the Daryaw « Chronicle of an older diver - July 7, 2009

[…] deco stop was the longest I’d ever done at about an hour, based on my Apeks Quantum’s calculations. Most of this was at 10 feet. We weren’t carrying any richer mixes with […]


9. Ken Blakely - July 5, 2010

I bought a Quantum when I was living in the UK, back in 2007, I think, and then I bought a 2nd for exactly the same reasons presented here – 1) have a backup comp that is exactly the same as the primary and 2) have the capability (if I wanted it) to dive >2 gasses. I’ve been quite happy with my Quantums, and I would recommend them to anyone who wants a good, solid, deoendable computer that’s easy to read and understand. My only real issues with these units stems from the Apeks PCLogbook software, which is pretty much crap, and the PC interface device, which is waaaaay too expensive. Oh, and I guess I should say that on both my Quanta, the right-side seawater sensor – the one over the B button – gets corroded. Donno why….


Chris Sullivan - July 6, 2010

For most of us they’ve lasted around 150 dives. Then something happens. We’ve had good luck with getting them replaced at no charge though, as long as they’re not too old. I’ve just sent my Shearwater Pursuit back to its birthplace to get upgraded to a Shearwater Predator. These are about 3x price of the Quantum but have Trimix, 5 gasses, colour OLED display, and can go several times deeper than I ever will. My main difficulty with the Pursuit was reading the display in the gloomy depths of the northern lakes and rivers, and the Quantum was easier to read, but the OLED display on the Predator is amazingly clear. It’s easy to read even when it’s on other people’s wrists.

I haven’t seen the corrosion problem, but most of my diving is in fresh water. Strange that it only happens on one side, maybe it the polarity. Agree with you on the PC interface. The Predator uses Bluetooth which costs around a buck to manufacture and is available on most modern laptop computers.

Thanks for sharing.


Chris Sullivan - July 19, 2010

So I was diving in Tobermory last week and my Quantum started acting up. It was fine at depth, but on ascent, after reaching about 40′ or so, the depth reading started jumping around. Specifically, it would show an instant ascent of about 10′, and then return to the actual depth. This played havoc with the ascent rate alarm and it beeped furiously for the final minutes of the dive. I’ve probably had it for about 150 dives, so it’s performance is up to par with others’ experience. This failure mode also appears to be quite common, although my first one just died.

Fortunately my upgraded Shearwater Pursuit (now Predator) has arrived. I can’t wait to dive it.


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