Dive computers - how conservative?

[scubadada]

But does the research show the Oceanic computers to be set to their normal mode or conservative mode of operation?
I would assume the research was based on the default mode of operation and since. Their is a conservative mode of opeartion built into the Oceanic computers which is not the default mode we really can't say the Suunto computers are any safer.

My incomplete summary of the model appears to have led to your misunderstanding. If you're interested, you may want to review the cited source prior to additional critique.

My comment had nothing to do with computer safety. The model simply estimates the probability of DCS events per 10,000 dives by using the maximum exposure allowed by the algorithm at 60 feet and comparing it to known rates from numerous observational trials. The exposure time used for the Pelagic Pressure Systems computers was 56 minutes and the exposure time used for the Suunto computer was 50 minutes. For further comparison, the 64 minute exposure allowed by the 1993 US Navy tables results in an estimated 110 episodes of DCS per 10,000 dives. The greater the exposure near NDL, the greater the risk of DCS.

I made a comment in an earlier post that I believe is cogent: "Personally, I think all of the available dive computers and NDL algorithms are quite safe. Whether you take a deep stop and/or a safety stop and the degree to which you push your computer toward the NDL, are your own choice. We must all operate within this grey zone of some uncertainty. Risk tolerance is a personal decision. A well educated decision is a good decision".

Dive safety is your own responsibility.

Good diving, Craig

 

[jd950]

You guys all make good points, and I agree the differences in algorithms for most people most of the time are largely theoretical. I also tend to believe more people expose themselves to increased risk by excessively fast ascents and skipped or blown stops than by diving close to their computer limit.

To answer gcbryan's question, I don't know when the conservative factor choice was added to Pelagic computers but all of their current computers have this. Essentially, by turning this on, the computer calculates NDL as though you were diving at 3000 ft above you actual elevation.

My impression is that on the OC1, the Pelagic z+ is very close to the Suunto in most situations, or perhaps is at more or less a midpoint between the Nitek and the Suunto? Essentially it gives the option of one of the most conservative algorithms or one of the most liberal, plus the addition of deep stops and a conservative factor, at least on the DSAT algorithm.

 

[Kern]

The Pelagic Pressure Systems/DSAT algorithm is the one I'm very fond of from my Pro Plus 2. The conservative Seiko algorithm (Dive Rite Nitek Duo, Zeagle N2ition, Tusa IQ-700 Hunter, Cressi Archimedes 2, Apeks Quantum...) is a modified Buhlman ZHL-12.
Craig

This put's the veracity of some of the data in the table at question.

 

[Web Monkey]

It is interesting, in most discussions on dive computers, there seems to be an implicit assumption that "the more conservative, the better". I tend to disagree. If the computer spits out something that it knows is too conservative, then it gives me inaccurate data.

Since they're all inaccurate (no table, algorithm or computer that currently exists, will perfectly model any specific diver), I'm not sure how you can say "Too conservative is inaccurate", or for that matter, even how you would even know if it's "too conservative".

There are people who get bent diving within the computer limits as well as people who show no ill effects diving well outside.

Terry

 

[TSandM]

I also tend to believe more people expose themselves to increased risk by excessively fast ascents and skipped or blown stops than by diving close to their computer limit

Yes -- the risk of DCS is a product of length of exposure time and choice of ascent strategy (and, of course, execution of that strategy). The minimum deco limits I dive are much more "liberal" than Suunto's NDLs, but also assume a certain ascent profile that does a "minimum" amount of deco.

Dr. David Sawatzky had a very interesting medical column in Diver magazine about two years ago, talking about the evolution of decompression algorithms. His conclusion was that the big step in reducing DCS came with Haldane's original model, and everything since then has been tweaking the far edges. The incidence of DCS is very low, and worse than that, many cases occur in people who have not violated their model at all -- which just says that the models are incomplete in their picture of gas dynamics in the body. So it is hard to point to any one model and say, "This is the one."

 

[scubadada]

This put's the veracity of some of the data in the table at question.

Sorry, I don't follow, what's this about?

Craig

 

[Kern]

Sorry, I don't follow, what's this about?

Craig

The table in the OP says at the head of the 8th column that the DR Nitec Duo is a Buhlman ZH-L 16, not ZH-L12 as you say (& I'm happy to accept) in the previous post.

Also

The NDL times for the PZ+ are slightly less conservative than my Dive Rite Nitek Duo but are much more conservative than the Oceanic algorithm to considerably deeper than 40 feet ( 50 feet 81 vs 65 minutes, 90 feet 24 vs 19 minutes...).

Craig

According to the info in the headers of the table, Columns 8 & 9 represent the computers you mention, & below 40' they are almost the same. From your description, they should show some variance.

So, are they incorrect pieces of information & if so are there more.

 

[scubadada]

The table in the OP says at the head of the 8th column that the DR Nitec Duo is a Buhlman ZH-L 16, not ZH-L12 as you say (& I'm happy to accept) in the previous post.

Also


According to the info in the headers of the table, Columns 8 & 9 represent the computers you mention, & below 40' they are almost the same. From your description, they should show some variance.

So, are they incorrect pieces of information & if so are there more.

Kern's post illustrates a very important point, check the accuracy of the information you post. The source I used in determining that the Dive Rite Nitek Duo used a Buhlman ZHL-12 algorithm is incorrect. I went to my owner's manual and, indeed, the computer utilizes a Buhlman ZHL-16 algorithm. I apologize for the inaccurate information. I was reasonably careful to post references for most of the other statements I have made in this thread.

On the other hand, the NDL times listed in the OP's table for the Nitek Duo are quite inaccurate, leading to the confusion in comparison to the Pelagic Pressure System's algorithm. The correct NDLs for the Nitek Duo are 40 ft 100 min, 50 ft 64 min, 60 ft 45 min, 70 ft 34 min, 80 ft 24 min, 90 ft 19 min, 100 ft 16 min, 110 ft 13 min, 120 ft 11min, 130 ft 9 min. This clearly illustrates the differences between the Buhlman and the PPS algorithms.

The Oceanic PZ+ algorithm (designated as Buhlman ZHL-16C) has slightly different NDLs than the Nitek Duo. Perhaps this is due to a different version or a modification of the algorithm. The OC1 values are all available from the owner's manual available on the Oceanic website. The PZ+ NDLs are 1-9 minutes longer for depths between 40 and 80 feet. Interstingly, they are all 1 minute shorter between 110 and 130 feet.

Thanks to Kern for bringing up these inconsistancies for clarification and correction. There's a lot of information available, some of it is accurate, and some of it is not. Verification is up to you.

Good diving, Craig

 

[Kern]

This has been bugging me a bit.

Why are the NDL's spat out for the Suunto a range of numbers. What does it mean by having a range of numbers instead of a specific number like the rest.

My Cobra never showed a range of times for the no deco time left.

 

[gcbryan]

This has been bugging me a bit.

Why are the NDL's spat out for the Suunto a range of numbers. What does it mean by having a range of numbers instead of a specific number like the rest.

My Cobra never showed a range of times for the no deco time left.

I guess it's just another problem with the table posted. The range for the Suunto's is dependent on how the conservative settings are used...why that same range of numbers isn't shown for other computers ...who knows?