Safety of some popular dive computer algorithms???

[DandyDon]

And there's the divers who violate their puters, so they remove the batteries so they'll work the next day!

I saw a newbie violate her's on a LDS trip, so the Instructor from the LDS loaned her a different one to use the next day.

And they blame the computers.!

 

[CuriousMe]

Certainly applies in my case, at my LDS. As a new diver, I bought a Suunto Vyper and the extent of the staff involvement in my learning how to use it consisted of pointing out the handy menu structure flowchart inside the back cover of the manual.

It required a good deal of study on my part to master all the features and all the displays--and I've designed computer interfaces, so I'm not unskilled at learning them.
<snip>

I also agree that the owner is responsible for doing the work of learning. But the shops don't help matters when they sell dive computers without stressing the need to master them before diving with them.

Bryan

The Suunto manual isn't the easiest to read....but it's not to bad and it's pretty logical in it's layout.

I guess I don't expect a shop to do that eponym....I don't expect the car dealership to show me how to use the mirrors on a new car....or anything else in there.....they're salesmen, not teachers.

If I'm a certified diver that walks into a LDS and buys a computer.....it's not the shops job to tell me I need to know how to use it before diving with it. They're not training me, they're selling me gear, it's my job to learn how to use it.

Peace,
Cathie

 

[DandyDon]

Some shops offer computer courses. Really good idea.

 

[DepartureDiver]

But how many scuba salespeople really understand what they are selling? When a consumer is trying to decide which one is best for them, they rely upon what they are told. This thread started with a question about the different models and algorithms. Most sales people could never answer this question. While I am sure they have some basic knowledge on half-times, this isn't enough to fully understand the differences in the computers, how realistic the modeling is, or how to use it as a tool. So how is a consumer supposed to decide which is best for them other than the salesperson's limited knowledge? And part of this knowledge is ease of use. While the salesperson need not go into all the details on how to program conservatism into a computer (for those that allow it), the basics should be covered on how to operate and read it so a customer can decide which computer to buy. I guess I'm on my soap box of wanting to raise the bar as to knowledge that should be given to a customer when they are trying to make such an important decision on equipment they are led to believe will protect them from getting a hit. Everyone gets the basic understanding that all regulators operate in a somewhat similar fashion with the more expensive ones being better. But when it comes to a computer, the internal workings can be different and most consumers probably never know how the times being generated by the computer are calculated and how realistic they are, yet they will completely rely upon them.

 

[DEEPLOU]

DepartureDiver
But how many scuba salespeople really understand what they are selling? When a consumer is trying to decide which one is best for them, they rely upon what they are told.

Minimal if any.

This thread started with a question about the different models and algorithms. Most sales people could never answer this question. While I am sure they have some basic knowledge on half-times, this isn't enough to fully understand the differences in the computers, how realistic the modeling is, or how to use it as a tool

I like to think I have read a fair amount on this, and quite frankly, I can't say that I have found much if anything on the safety of one computer's model / algorithm compared to another.
Recent article did compare several computers using different algorithms and models. It showed how the different algorithms gave different readings (vastly different) but it did not comment on the "safety" of one compared to another.

But when it comes to a computer, the internal workings can be different and most consumers probably never know how the times being generated by the computer are calculated and how realistic they are

And they never will know.

How realistic?? Its all theory!

I've seen so many folks get on a dive boat and then try and figure out how to use their computer.....some don't even have the manual with them!

Some don't even have the manual?? I have found that MOST don't have the manual.

Most computers are not that hard to figure out.
Several times (in resort areas) I have had to give "learn your computer 101" on the way out to the dive site.

 

[Daryl Morse]

Hi Doc,

I'm in a similar position to Austin. I'm a new AOW diver doing some "research" as part of looking for my first computer. I plan to take an introductory nitrox course next year and eventually also get more advanced training involving decompression diving when I accumulate enough experience.

I read the same article in Scuba Diving and it evoked similar questions. (Just to be clear, I don't consider Scuba Diving to be an authoritative or unbiased source of information.)

Algorithms
There are basically only two algorithms (= calculation methods) in dive tables and computers today. The “Two phase” algorithm (RGBM and VPM) allows for bubble nuclei and takes into account the Laplace pressure in the microbubbles from surface tension. The other is the “Haldane method” that tracks only dissolved tissue gas loads. For all of the algorithms, there are additional constants that control certain factors related to tissue gas loading and ascent.

The differences between the algorithms within the Haldane group are the constants, the ascent limits or “no decompression limits”[NDL] and supersaturation limits (M-values). Variations in these will allow for the construction of both a very liberal or very conservative table (and dive computer) and anything in between.

Do you lump the DCIEM algorithm in with the Haldanean algorithms? Based on the article, it seems like it makes some pretty different assumptions.

What is the best source of information for a "lay person" to learn about decompression theory? My education isn't in this field (I'm an electrical engineer), but I'm technically inclined and very interested in learning more about this topic. If you can point me at some books or research papers that are available on line, I'd appreciate it.

Computers

As I see it, it matters little which computer you use since all have constants that have been shown to be safe for recreational diving.

What is not said is that the constants are arrived at by testing divers in a laboratory where physical activity is minimized; the diver test subjects mostly just sit around in the lab. The constants in the table would be different if the divers were required to perform some strenuous activity before the chamber dive (to simulated hauling dive gear) and simulate strenuous active post chamber dive (to simulate climbing ladders, moving tanks, etc). No table would ever be test with the subjects playing beach volleyball.

If you believe that you will be hauling gear around post dive, I would suggest a meter allowing on conservative gas loads - and then maybe staying away from the limit. Deep diving with decompression would be better served with meters that have a dual phase model.

Like Austin, I was quite surprised at the differences between the computers as tested by Scuba Diving. The biggest area of difference was in the second dive which was a reverse profile. The Citizen computer (DCIEM-based) went from being the most conservative to the least conservative. It gave back 63 minutes of NDL after a 4 minute ascent from 60 fsw and 7 minutes at 40 fsw. By this time, it showed 66 minutes of NDL whereas the Dacor and Mares showed 0 and 1 minute of NDL, respectively.

If all of the computers are "safe" for recreational diving, then is it reasonable to say that some computers are overly conservative in certain circumstances or that some computers are building in less room for extraneous influences such as water temperature, post-dive physical exertion, etc, or do both apply?

 

[ekiledjian]

Hey, I'm a AOW diver who's training for my Rescue and Nitrox cert, and i'm looking into getting my first dive computer. I really want a hoseless model, and have been doing some research lately into the different algorithms the different computers use. I picked up a copy of August "Scuba Diving", in which scuba lab tested 11 top dive computers. They put the computers in a Hyperbaric chamber to simulate 3 repetitive dives.

Some of the computers, based on their algorithms, added a lot of no-deco time as they ascended from the max depth. The computers that added the most deco time, almost twice as much as the others, were using the Haldanean Algorithm: which groups the bodies thousands of different tissues into theoretical tissue compartments, each with a different rate for absorbing and releasing inert gas. It also states that gas was always released at the same rate at which it's absorbed. As I'm sure many studies have proven, and which Scuba Lab confirmed, it's a very liberal algorithm.

Scuba Lab believes its a very liberal algorithm when its compared against the Buhlmann Algorithm and the DCIEM Algorithm and especially the RGBM (Reduced Gradient Bubble Model). Scuba Lab says that this Algorithm was developed after Doppler bubble research showed that "silent bubbles" unknown to the Haldanean algorithm often form after a dive without causing DCS symptoms. On the theory that these bubbles would be slower than dissolved gas to leave your body, and could even interfere with the outflow of dissolved gas, the RGBM algorithm is very conservative.

I'm very intrested in the AERIS Atmos Elite and The OCEANIC VT PRO wrist mounted, hoseless dive computers, my concern is that they borth use the Haldanean Algorithm, which at some points on the last dive, gave 74 minutes of no-deco time when ascending, while the RGBM gave 30minutes of no-deco time.

In conclusion, i want a safe computer, but not a paranoid one. Based on these different algorithms, is it okay to add that much no-deco time when ascending? Which algorithm or theory is correct? I don't intend to pretend that i know a whole lot about this subject, i've just read the Scuba Lab's results and some other material. Thanks for your responses, i know this is kinda long...

I use the Suunto Stinger. It uses a modified Suunto RGBM algorythm that I believe is safer than the DCIM od Heldane models. Plus I can wear it as a regular watch and that way I know no one will "borrow" my watch on a dive trip. I spent 3 months searching before I bought it. Take a look at:

http://www.suunto.com/suunto/main/p...older_id=9852723697223379&bmUID=1095023402740

I bought it from http://www.divetank.net. They have a great price with the computer interface and a super warranty.

Good luck,

Ed

 

[Derek S]

I too am in the same boat as Austin and Daryl. I'm basically trying to decide between the Atom 1.0, VT Pro, Atmos Elite or Vytec. I don't particularly like the way a Vytech goes about it's business, and the manual, while informative, feels like I'm reading it in another language. I'm a technical person by nature, but it just isn't very well written IMO.

One thing I think I've learned through all of this is that a dive computer is only as smart as the diver using it. There's an old Army saying, and I find it particularly pertinent here: "You need to be 10% smarter than the equipment you're trying to operate."

While I do plan to go air-intergrated, I will continue to use my mechanical SPG/Depth gauges as back-up on every dive. As Don said, plan your dive and dive your plan. The dive computer I ultimately chose will (for quite some time at least) be nothing more than a glorified digital depth/temprature/PO2 gauge. I will be sure to do dives that will keep me well within NDL/PO2 limits based on my PADI tables, and plan to do 3 minute safety stops on any dive that exceeds 30 feet.

 

[ThatsMe]

Wow alot of good information in this thread,

 

[Life-Is-Good-Diver]

I wouldn't ho by Rodales report, The models will vary depending on diving parameters.. RGBM penalizes the diver on repetitive profiles, while normal Haldane models do not..

BTW the computers you mentioned and ALL the ones tested by Rodales are Handane models.. The difference is that some have RGBM limiting factors folded over them.. If you want a TRUE RGBM cmputer buy the HS-Explorer (Its expensive)..

On simple NDL profiles times are pretty close, once you get into mandatory decompression stops Bubble models (VPM, FULL - RGBM) tend to get you out of the water quicker and in some case ALOT quicker..

I do dives with students decompression students all the time many carry Suunto dive computers, when we do the dives against true RGBM tables and verified by my explorer we generally will "bend" the Suunto computers as they want ALOT more deco than the tables predict..

You hit it right on the nose, as i use the HS explorer, and also have a Vytek, i actualley have 4 computer,s now that my wife is diving, i love the HS, i dive with alot of Tech diver,s, and seen them all goto the HS explorer one time or another, the Suunto computers will "bend" and take alot, i mean ALOT more time to clear you, then the HS, but in my opioun, the Suunto is a great computer for under the $500 range, if you plan on spending $1,000.00 , then i love the HS, it's a great computer.