So you want to buy a new computer?

[kelemvor]

You may have missed the fact that the post you quoted that refers to computers that do not do nitrox was written in September 2009, nearly 7 years ago.

Yup. It came up in my "new posts" search. I guess because someone replied, and now I've also replied making it worse. One of the hazards of scubaboard, I guess.

 

[SandyUT]

One of the questions that seems to get perennially asked on SB is “what computer should I buy?” or “New computer advice needed!” There are far greater experts on SB than me (hopefully they will chip in with their own views and advice), but I thought it might be useful to try and collate the gist of the responses that tend to come forward every time this question is asked:

First and foremost, it is your choice. And you should make it based upon the considerations of your own diving plans, now and for the future. The question is usually asked by new divers, so think about it: where is my diving likely to go? Am I going to use nitrox soon? Am I just an occasional weekend diver? How much do I want to invest in this (at the expense of other gear)? Sadly for new divers, there is no real “gold standard” dive computer that everyone uses. You will need to make a choice from a bewildering large array of options.

What are the factors you need to consider? Well, the main ones are:

Computer vs no computer? The first question is do you really need a computer at all? If you are not going to engage in repetitive diving, or particularly deep diving, then provided you can follow the basic table limits, investing in a computer may be unnecessary anyhow. Conversely, at the other end of the scale, some very advanced divers (specifically those who adhere to DIR philosophies) eschew the use of dive computers, preferring to focus on careful dive planning. That being said, there is probably a very large majority of the diving world between those two poles who use and value their dive computers.

So, if you do decide to get a computer:

Wrist mounted, console or HUD? Some people prefer to have the dive computer mounted on their wrist, others prefer it on their console next to their SPG so that all of their information is in one place. However, if the computer is air integrated with a wireless transmitter, one can still have all the relevant information in one place on your wrist. A comparatively recent innovation is HUD, or “head’s up display”, dive computers, which is jargon for “inside the mask”. Although it makes for a bulky mask (and an expensive one if you lose it), it does mean that even in literally zero visibility and complete entanglement, you can still read your gauges. Everyone has their own preferences, but wrist mounts tend to be more popular with advanced divers, not least because it does not need to be fixed to a single regulator.

Air integrated or not? Many dive computers have air integrate (“AI”) pressure gauges, so that they can monitor your air and predict your remaining “air time” based on rate of consumption and depth, as well as your remaining no decompression limit. The advantage of this is that the computer can monitor and warn you as to your maximum dive time, both due to remaining air and remaining NDL. However, others suggest this ingrains bad habits - relying upon your computer rather than learning to check your remaining air regularly.

If the computer is not a console computer (ie. it is either wrist mounted or HUD), then to be air integrated the air pressure must be transmitted by a wireless transmitter. Whilst this is a neat gadget, they do have a reputation for being flaky, and so normally divers will carry a separate conventional SPG as well.

Air or nitrox or even trimix? All dive computers track your no decompression limit on air, but the cheaper ones can only do air. More expensive computers can also calculate your limits for enriched air nitrox. If you are likely to progress into nitrox, you may want to consider this additional investment. This is probably the biggest decision to make, as having a nitrox enabled computer usually involves the first significant step up in retail price.

However, even amongst nitrox computers, there are distinctions between those which require the dive to be calculated entirely for one gas, and computers which permit “gas switches” used by technical divers to accelerate decompression. Interestingly, it doesn’t follow that all technical divers use expensive nitrox gas switching computers - Rhone Man recalls when he was learning technical diving, he was speaking to some very experienced technical divers on the boat, and they each used a pair of cheap “air only” computers, even though they used highly enriched nitrox to accelerated decompression. They reasoned that the computers were just a backup, they were cheap, and they wanted the safety factor of knowing they would have been safe even if they had been breathing air the whole of their decompression before ascending.

There are also a small handful of computers which can calculate decompression profiles for trimix and other helium mixtures as well, although these are expensive and it must be very rare that a new diver anticipates getting into trimix diving without substantial further expenditure in equipment and training. Even divers who engage in trimix diving debate whether having a trimix computer is actually useful, given the complexity of trimix decompression schedules.

User replaceable battery or factory replaceable battery? On the face of it, having a dive computer where you can change the battery yourself looks like a huge plus. But there are downsides. User replaceable batteries tend not to last as long as factory replaceable batteries, so you find yourself replacing the battery more often, and the battery usually runs out at the least convenient time possible. Also, there is a bigger risk that you might do something wrong when changing your batter, your dive computer will leak and find a new function as either a paperweight or a door stop.

How conservative? Not all computers are rendered equal. Some computers have are more conservative, and allow shorted no decompression dives. Some dive computers penalise you heavily for skipping the safety stop, or ascending too fast. Others are much more relaxed. Some computers allow you to set it to be more conservative or less conservative.

Below is a table which tries to compare how relatively conservative the main brands of computers are:

However, be wary of putting too much stock in this point. The main benefit of computers is not for a single dive, it is for repetitive dives. All computers are more generous than the tables, because tables rely upon just one tissue group to calculate the benefits of a surface interval, whereas computers will track all, and thereby maximise your benefit.

I dive with two computers - a Suunto (very conservative) and a Sherwood (very aggressive). Frequently the Suunto tells me that I am in deco whilst the Sherwood assures me that I can surface at any time. I just treat it like a long safety stop and don’t worry unduly.

Price. Dive computers vary enormously in price - new computers can be as cheap as $200 for basic models, to as expensive as $1,500 for very sophisticated computers. Some people advocated that you buy your “last computer first” - and go for the most expensive model that you ever likely to need. Others (including me) would suggest starting with a cheaper computer, and then upgrading when you need something more sophisticated (prices keep coming down, and quality keeps going up - waiting often has advantages).

New or second hand? Opinions vary hugely about buying second hand computers. One thing is certain - there are some very cheap second hand computers available on eBay, particularly if you are willing to put up with some cosmetic scratches (I bought my Suunto once for about 1/3rd of retail price). However, as lawyers say: caveat emptor - buyer beware.

Functionality / attractiveness. Some dive computers are sufficiently small that you can get away with wearing them as a watch. Sort of. A big chunky watch. Still, some people value that - if you wear your dive computer as a watch, then you will always have it with you if a diving opportunity suddenly arises unexpectedly.

Models. There are many, many different models of dive computers. It is impossible to run any kind of meaningful comparison, but according to the kind people at Wikipedia, this is a list of the most popular models (by market share):

* Suunto (31.6%)
* Oceanic (27.0%)
* Aeris (11.9%)
* Uwatec (6.6%)
* Mares (5.3%)
* Cressi-Sub (3.8%)
* Sherwood (3.5%)
* Scubapro (3.1%)
* Genesis (2.8%)
* Tusa (2.0%)
* Aqua Lung America (1.3%)
* Seaquest (0.8%)
* Zeagle (0.2%)

Good luck!

This info has been priceless!!' I used it to find cross compatible parts between aeris and Sherwood. Many thanks!!!'

 

[flyboy08]

Cressi Leonardi....

Just used this computer obtaining my AOW. We did deep dives and multi level dives and the computer was flawless. I was concerned about reading it being over conservative, but it wasn't in any respects. In fact, based off of two orher computers ( sorry didn't get names), the Leonardi was less conservative at depth below 100 feet.y

Some have also complained about excess beeping, but if you listen to the computer...ie, ascend accordingly, it doesn't sound off.

For the price, this piece of equipment works for my diving style and I do like the single button as well.

Just an FYI.....

 

[HonuGayle]

Thank you, Rhone Man! I last bought a dive computer six years ago and need a new one. Your detailed guide answered a lot of questions and is very helpful. BTW, my third ever dive was The RMS Rhone in 1981 with Blue Water Divers. Wonderful BVI trip on the Flying Cloud.

 

[urbaneve71]

Thank you so munch for the information. I have been diving since 2002 and this is the first time I have considered an air integrated system. I will have to re-read this post again as there is so much information. Thanks to all those that contributed outside links to help me decide. Even though I am still up in the air about what to buy, this post does help me narrow it down quite a bit.

 

[stuartv]

I sent this out (somewhat paraphrased) in an email to some friends earlier today. I thought it might be worth also posting here, for posterity.

Caveat: Some of this is really only relevant to Rec diving to NDLs, so take away what is useful to you and ignore the rest.

On algorithms:

Here is a link to a post from RonR, who IIRC (I *think*) from other posts is an engineer at Atomic Aquatics. The summary is that different computers can implement their algorithms differently, even if they are “the same” algorithm. So for example, one computer that implements Buhlmann ZHL-16C might still give you a different dive profile than another computer that also implements Buhlmann ZHL-16C. Needless to say, computers with different algorithms (Buhlmann, RGBM, VPM, Haldanean/DSAT, etc), can give very different dive profiles.

Read RonR’s post for the full explanation:

http://www.scubaboard.com/forums/co...-leonardo-too-conservative-4.html#post7342293

I think it’s also worth noting that many computers use a proprietary implementation of their algorithm. So, attempting to predict what the computer will do by modeling your plan on your desktop computer may or may not produce exactly the same results, for the same reason above. The best way to be assured of the best match between desktop computer and dive computer is by using the desktop software that is provided by the OEM of your dive computer (IF they do in fact provide any). Aftermarket software, for example V-Planner, may use the same algorithm as your dive computer, but it could still be implemented differently, thus giving you a different dive profile.

On conservatism:

The first post in this thread has a simple chart comparing 1st dive NDLs for a variety of different types of computers. One example from the chart: At a depth of 100’, USN and NOAA tables allow 25 minutes, PADI RDP allows 20, the most liberal dive computer allows 19, and the most conservative dive computer allows 8 minutes. Of course, pretty much any dive computer will let you adjust it to make it more conservative, so you CAN use the most liberal computer and still have it limit you to not come so close to the PADI 20 minute limit (as one example), if you want.

However, my research convinced me that looking at what the computers do on repetitive dives in the same day is at least as important to look at. For that, Scuba Magazine did a couple of good articles where they put all the computers they were testing into a hyperbaric chamber and replicated doing 4 dives of different profiles, with surface intervals in between. They logged the NDL shown on each computer for various simulated depths.

Their 2014 test results are here:

http://ads.bonniercorp.com/scuba/PDF/ScubaLab-Computer-Test-September-2014-data.pdf

which is from this article: SCUBALAB 2014: Dive Computer Review - Page 2 | Scuba Diving

As one example, this test shows a 1st dive to 100’, then a 60 min surface interval, then a second dive to 70’. After EDT (Elapsed Dive Time, on the 2nd dive) of 18 minutes, at 70’, the most liberal DC shows an NDL of 20 minutes and the most conservative shows 12 minutes. The differences are even bigger when the diver starts to ascend some and spend time at shallower depths.

The differences get even more dramatic on the 3rd dive, which is after a 120 minute SI, to 80’, then gradually working up to 40’. After EDT of 36 minutes, at a depth of 40’, the most liberal computer allows 56 minutes of remaining time before the NDL, and the most conservative allows 2 minutes.

56 minutes versus 2 minutes is a pretty big difference!

Scuba Magazine’s test results from 2007 (I think) are here:

http://www.scubadiving.com/files/old/images/pdf/scubalab_200706_10_new_comps.pdf

which is from this article: dive computers: scuba gear reviews | Scuba Diving

This one is kind of more of the same, but with some different computers, as the first article.

I hope this helps someone as much as finding it all helped me when I was shopping for my computer.

RonR just posted another very insightful post regarding the implementation of algorithms in dive computers and how they can vary based on choices the implementer makes, while still complying with the actual algorithm. I think it's worth also adding a link here, for posterity.

http://www.scubaboard.com/forums/co...uter-divemaster-internship-4.html#post7388301

I can no longer edit those old posts, so I'm quoting them here to keep all the info in one post.

The ScubaLabs 2016 computer review and lab tests is out (has been out). The review is here:

11 New Dive Computers Tested and Reviewed By ScubaLab

The direct link to lab results is:

http://www.scubadiving.com/sites/sc...achments/2016/09/2016_chamber_worksheets.xlsx

My quick-and-dirty assessment of the lab results is that it looks to me like:

- The Perdix in OC Rec mode, set for Low Conservatism, gives NDLs very much like the other computers that are running the DSAT algorithm (e.g. Sherwood and Oceanic).

- The Cressi Newton and Suunto computers in the test seem to now be giving NDLs very much like the other computers that are running the Pelagic Z+ (aka PZ+) algorithm (e.g. AquaLung and as an alternate algorithm on the Oceanic computers).

NOTE: You cannot compare NDLs for Dives 2 - 4 from the 2016 lab test with NDLs from the previous years' tests. For whatever reason, the last segment of Dive 1 was done differently in 2016, ending the dive about 12 minutes earlier than Dive 1 of 2014. So, I think NDLs can be compared for Dive 1, between 2014 and 2016, but not the later dives.

 

[Tibbers]

thanks.i just want to buy a computer, considering which one i ll take.

 

[kevinutah]

I just purchased an Oceanic VTX color display computer late in 2016. The VTX is now being returned- the screen that looks so nice in a dark room, is useless in daylight setting, even when set on 100% brightness. In clear water, you still cannot read the display at most depths to say 90 feet without cupping your hand over the display. Also, after just 5 days of two tank dives, the new batteries again needed to be changed in the wrist computer (transmitter was Ok). Because of the battery problem (posted all over the net in reviews), and especially the screen that is black background and color text making it impossible to really use. I not only would not recommend this computer, but actually think Oceanic should recall the VTX as it is mostly useless in typical daytime diving settings. I may try the OC!, but worried after Oceanic put this VTX out being so useless.

 

[!@#$%^&*()]

I used to believe in cochran dive computers. However, a recent event has shown me they are so desperate for you to buy one from them they will use any excuse to not repair it. The model I own is one still in production but is an older computer and last year I asked what the cost of a repair was ( I cracked the lens )....I got 2 different answers and finally a Tony emailed me and said that they would look at it. Due to an injury at work I could not send it in until recently when I got a short terse answer they would not repair it but I needed to buy a new one. Keep in mind I bought mine when 3K + depending on color and attachment was the price for the EMC-20H with 3 FO2 / 2 PO2 + He . They are very proud that they dropped the price to 600, however as someone who paid full price for one, I not only feel duped, but I think there is a different reason for the change. Because everyone would not overpay 2400 buck for this computer, they shopped for a better priced one. I saved all of the emails so when people ask, I can show them.
I am now shopping for 2 new dive computers. I always dive with 2 so I have a back up. The above listed information is well timed for me and I am sure its appreciated by all. As for cochran, I will not support them anymore. This hurts because I like buying American, but overpaying the first time, then getting sarcastic emails later, and now a refusal has shown me the light.
Dive on!!!
BTW, anyone that is currently using a larger sized, tech computer that will do multiple gasses, I would love to hear on this thread what you like and what you don't like as well as any support issues you may have had. I think many divers, both old salty dogs and the newly indoctrinated would find this important information to assist them in any future purchases. At this day and time I do not think ANYONE needs to only dive tables, but use a dive computer and use the tables for back up and planning. My personal opinion as someone who has dove most of my life.
Thanks!

 

[Dive Cochran]

I used to believe in cochran dive computers. However, a recent event has shown me they are so desperate for you to buy one from them they will use any excuse to not repair it. The model I own is one still in production but is an older computer and last year I asked what the cost of a repair was ( I cracked the lens )....I got 2 different answers and finally a Tony emailed me and said that they would look at it. Due to an injury at work I could not send it in until recently when I got a short terse answer they would not repair it but I needed to buy a new one. Keep in mind I bought mine when 3K + depending on color and attachment was the price for the EMC-20H with 3 FO2 / 2 PO2 + He . They are very proud that they dropped the price to 600, however as someone who paid full price for one, I not only feel duped, but I think there is a different reason for the change. Because everyone would not overpay 2400 buck for this computer, they shopped for a better priced one. I saved all of the emails so when people ask, I can show them.
I am now shopping for 2 new dive computers. I always dive with 2 so I have a back up. The above listed information is well timed for me and I am sure its appreciated by all. As for cochran, I will not support them anymore. This hurts because I like buying American, but overpaying the first time, then getting sarcastic emails later, and now a refusal has shown me the light.
Dive on!!!
BTW, anyone that is currently using a larger sized, tech computer that will do multiple gasses, I would love to hear on this thread what you like and what you don't like as well as any support issues you may have had. I think many divers, both old salty dogs and the newly indoctrinated would find this important information to assist them in any future purchases. At this day and time I do not think ANYONE needs to only dive tables, but use a dive computer and use the tables for back up and planning. My personal opinion as someone who has dove most of my life.
Thanks!

Cochran NEVER charged you 3K+ for your 20H
Your dive shop where you purchased it screwed you and that's why Cochran has gone to direct sales so we can control the price and all warranty issues. When you say your 20H is older exactly how old is it. Please forward your emails and Tony's response (s) to me and I will definitely find out what the issues are. jvc@DiveCochran.com
Also could I please have the serial number of your 20H.
Thank you

Have a great day
Safe Diving
John

Sales Manager Worldwide
Richardson, TX
www.CochranMilitary.com