Computer vs Algorithm
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Check here: VVal-18 and VVal-18M Thalmann Algorithm Air Decompression Tables and Procedures.
I read it again quickly (it's been a while) and I think the report gives a more nuanced picture than my post did. The conclusions that I found particularly relevant are found in paragraph 7.2
R..
I think the discussion boils down in part to what type of nerd you are. Are you an equipment nerd or a fish nerd? Stuartv is an equipment nerd. I am a fish nerd. I have equipment that works. My time and efforts are spent looking at the fish and animal life in the ocean. I do not change equipment unless it is getting unreliable or ticks me off. (Bye Bye Suunto). Those interested in tech diving tend to be equipment nerds. My goal is to be relaxed under water so I prefer benign dives with long NDL. On SB there are a lot of equipment/tech types. Among the general diving population there are a lot of both types.
Carlos Lander
Registered
Please Read carefully:
Thalmann Algorithm Schedules for air-only decompression prescribed by either the VVal-18 or VVal-18M (modification for SurDO2) Thalmann Algorithm are recommended with less enthusiasm because such schedules prescribe large decompression time increases that afford only relatively small DC risk decreases from those incurred by current procedure...
Thalmann Algorithm are only available on Navy computers, if anyone are interested, read the papers available, but make informed opinion over it, it may confuse people looking to understand those papers.
EMC-20H public released has a proprietary algorithm with bubble compensation tested in many occasions.
Although the computer still maintain a military mindset with automatic switch -that not everybody understand nor -not- know how to use it.
If anyone is interested on it, call me or call Cochran directly. Always search for primary sources of information and make informed decisions.
My best to all,
Note:
For disclosure I'm user and seller from Divesoft and Cochran user .
Last edited:
Jeff Loudan
Registered
John,
I went to your site as I had never heard of your computer before. Very interesting.
My question is what makes your algorithms better?
Also I am curious about your sample population for the research behind your algorithms. Was it predominantly Navy SEALS, extremely physically fit divers performing strenuous activities? How does this relate to your typical non-commercial civilian diver?
Not bashing just curious...
Hi Michael,
Thanks for your interest in Cochran dive computers. There are obvious proprietary issues that come into play when discussing the algorithms in our computers. To put it as simple as possible, our algorithm is designed to give the maximum bottom time, with an aggressive decompression schedule for safety. The individual diver may also adjust any of several different environmental compensations to 'tune' the algorithm to fit the diver's current physical condition and the conditions of the upcoming dive. As for your questions regarding the testing populations and how they relate to a civilian diver, I'm not sure how to respond. Granted, the Navy divers are more fit and do engage in rather strenuous activities, but I can't see a correlation to recreational divers, especially given the significant differences in diving skills between the two. Hope this helps, but feel free to reply if you have any further questions. Have a great day and dive safe !!
Jeff
I did, but you need to read further than the abstract. In the conclusions, point 7.2.1 the text reads:
7.2.1. Estimated DCS risks of Air-only schedules prescribed by the Thalmann Algorithm with either VVal-18 or VVal-18M increase with increasing bottom time in each dive depth group. Unacceptably high risks are attained with sufficiently long bottom times in most groups. The maximum risk attained in tabulated VVal-18 Air schedules is about 9%, substantially lower than highest risks incurred by USN56 schedules. The maximum risk attained in tabulated VVal-18M Air schedules is about 11%.
As I'm sure you know NEDU defined a "acceptable" risk of DCS in their tests as less than 5%. Both 9% and 11% are higher than 5%.
I also said in the post there I posted the link that the report was more nuanced than I had been in my post before that. I may have been (probably was) a little selective in what I remembered from the first time I read this report.
The report seems to be saying that the algorithm is safer than the air tables, that the DCS risk is generally very low but that the decompression times calculated are very long. For example, in one of the tables (working from memory again here) there is a dive listed that show a typical model (probably the air table) give a run time for a dive of 120 minutes while the Thalmann algorithm gives a run time for the same bottom profile of about 300 minutes. That's what they mean when they are saying long decompression times. The conclusions about the algorithm for long dives is that the DCS risk appears to fall out at higher than 5%.
That's what I get if I read the whole article.
R..
Which is exactly why I do not like the Cochran computers. Tell me how it works, or don't try and sell it to me.
Quite a number of computers use proprietary algorithms. While they may not be bad (or may even be good) the problem for a technical diver is that they have not been validated scientifically. Like you, I wouldn't use an algorithm lacking scientific validation but that doesn't mean that the computer in and of itself is bad. Lots of people use Mares and Suunto computers too and nothing could be more mysterious than the algorithms being applied.
For divers engaged in no-stop diving I wouldn't see any particular objection to using proprietary algorithm provided it was generating NDL's similar to a validated algorithm. What is also clear in the technical realm is that all algorithms drift to higher risks of DCS the longer the dive gets. The question then becomes at what point the algorithm can't be trusted anymore. The problem with un-validated software for technical divers is that you're left having to search for a feeling on that point by how you feel after the dive. I don't like that idea.
R..
In what way has Buhlmann ZHL-16C been validated scientifically that the Cochran algorithm hasn't?
In my mind, the scientific validation of Buhlmann has been amassing large amounts of data about dives done using the algorithm, showing that is produces DCS within a tolerable limit. Has the algorithm Cochran uses not had a similar treatment?
Or do you mean something else when you say "validated SCIENTIFICALLY"?
As a technical diver, my issue with the algorithm is not whether or how it has been "validated". My issue is whether it has been publicly disclosed, so that it can be implemented by an independent developer. I feel that 2 completely separate and independent implementations that produce the same results are more trustworthy than, for example 2 separate implementations from the same source - e.g. a dive computer and desktop planning software that both come from the same company. They could both produce the same results because they both have the same bug in their implementation. That is also why, awesome as they and their products are, I would prefer to not (and don't, actually) dive 2 Shearwater computers.
You're using the word validated differently than I am. What you are talking about is a technique by which software can be validated as being correct to specifications. I'm talking about validation as being fit for purpose in the context of previously researched results with corroborating evidence to link them to a particular level of DCS risk.
R..
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