Why do some agencies recommend using a bottom timer instead of a computer

[boulderjohn]

I also understand that it is a bit hard to be in your position. I was interviewing a very famous shark researcher once and he said the words, "In the light of what we understand today, Great White sharks may not be as dangerous as we previously believed." This interview was re-purposed by many news agencies around the world. The headline that went on many of the affiliate news networks was, "Great Whites are NOT that dangerous!" says the scientist!" You will notice that this is exactly the same mistake that I made while quoting you but this particular scientist never bothered to come after the networks to have it "fixed." The misquote was totally in line with major public sentiment on sharks so the scientist never bothered.

actually, the two are not the same. The shark scientist was not concerned because even though it was a misquote, that misquote was in line with what he actually believed. In this case, however, the misquote conveys a meaning close to the opposite of what is believed.

 

[Diver0001]

I will be sure that in the absence of hard scientific evidence, all my future misquotes are in line with popular public sentiment

Due to the nature of my day job we get in the papers on a regular basis and seldom (to never) positively. My view of journalism has perhaps been formed by this but in my opinion most journalists deliberately misrepresent the facts and many lack an ethical compass.

R..

 

[Dan_P]

Dan seems to be saying, in contrast, that any strategy that ever works is equal to any other system that ever works, because all are effective.

No. I'm saying that if "imperfect" equals "ineffective", then all strategies and algorithms but one are "ineffective" under the logic in the following quote by @Diver0001 specifically to show how that's not the case. You seem to agree with me.

It should be noted for the record in case anyone reads this and naively thinks that you're speaking the truth, that ratio deco is NOT an effective tool if you consider "effective" to mean that it gives you the optimum chance of avoiding DCS.

However, I think there are two important notes to make on this particular offshoot;

1) I think it's a separate matter from a conversation on the merits of a standardized decompression/gas-paradigm, i.e. "Why do some agencies recommend using a bottom timer instead of a computer?".

2) I think, given the scientific basis available at this time, the risk is probably blown out of proportion in the arguing against RD; as for what can be said whilst claiming to be in lieu with available science, I find this quote agreeable;
(underscore added for emphasis)

If you did the same decompression time, but distributed your stop time shallower, then you would almost certainly have less risk, The actual difference in risk might be relatively small, and perhaps not worth arguing about. Nevertheless, if people seek the truth on the path to least risk for the same decompression time I very much doubt that RD2 is the answer!

I would add that what we're talking about here, is the standardized, formal framework, prior to personal adaptation (for instance to reduce deep stop emphasis).

On a final sidenote, I personally think that claiming RD2.0 is "dangerous" (or similar) can't be said to be a science-backed statement.
Paradoxally, statements to that effect seem to have a trend of claiming to be just that.

In a hope to get the conversation back on the track of why agencies would offer a standardized deco/gas paradigm such as tables or ratio deco, and the use of bottom timers;

I think that for a lot of people with strong opinions on the matter, it would make sense to ask rather than state - especially if incorrect!
Ratio deco was made in a time where the (lack of) availability of good computers was a real motivation - but that is not a motivation for contemporary application.

The following exchange touches on one such motivation;

• The math required to do Ratio Deco is not that big a deal. Anyone can do it with ease.

• The people who make mistakes with Ratio Deco and get bent were not properly trained. A couple years is jot enough.

If you make 3 serious errors during a dive and you and your buddy don’t notice the errors you shouldn’t do the dive.

If you make 3 serious errors during a gas switch and you and you buddy don’t notice it there can also be a seriously problem.

Also when you and your buddy do a cave dive and make 3 serious errors with navigation.

I think it is wrong to ignore the fact that they shouldn’t do the dive. Training would be the solution, not buying more advanced equipment.

@barth really hit the nail on the head with this.
It's possible to mask transcendence of one's comfort zone, with equipment, but I'll say with some confidence it's generally not a good idea.

Ratio Deco really isn't heavy to manage - very roughly put, light juggling of the 3-table, but you do have to be able to think.

In light of that point, which I think we should agree to be self-evident, I feel it's fair to point out that one's deco planning doesn't begin at the end of the bottom time/beginning of ascend - one ought to either be well ahead of that, mentally, or be doing simpler dives.

To me, Ratio Deco helps drive and develop the thinking diver.
That is a motivation for it's contemporary use.

 

[boulderjohn]

2) I think, given the scientific basis available at this time, the risk is probably blown out of proportion in the arguing against RD; as for what can be said whilst claiming to be in lieu with available science, I find this quote agreeable;
(underscore added for emphasis).

You evidently missed post #86, in which Dr. Mitchell takes Captain Sinbad to task for mischaracterizing that same quote in the same way you did.

 

[Dan_P]

You evidently missed post #86, in which Dr. Mitchell takes Captain Sinbad to task for mischaracterizing that same quote in the same way you did.

On the contrary.

I took note of Dr. Mitchell's post on that matter, which is where you'll find the quote I added in my post. I have added that post in quotation at the end of this one.

There is a serious gap between the available science and any claim that RD is "dangerous", or similar - hence I put that any such claim would be unscientific.

I personally find that paradoxical as, in my opinion, many posts claiming risks or dangers of RD seem to also imply, state or have basis in a position that its use must be driven by disregard for precisely science.

Here is the post I quoted from;

Hello CSB,

You are misquoting me. I hope this is just clumsy rather than intentional. The exact text I wrote in my PM to you was:

If you did the same decompression time, but distributed your stop time shallower, then you would almost certainly have less risk, The actual difference in risk might be relatively small, and perhaps not worth arguing about. Nevertheless, if people seek the truth on the path to least risk for the same decompression time I very much doubt that RD2 is the answer!

This is a much more cautious interpretation than implied by the black and white terms you are using to describe what I said. We have not accurately measured the actual difference in risk between the approaches one could characterise as "RD2 deep stops vs something shallower", and so my statement is simply a case of scientific honesty. But I very intentionally used the words "might" and "perhaps", and you will note the final phrase in which I state "very much doubt". I would appreciate it if you could try to be more accurate when quoting me in future.

Simon M

 

[Ayisha]

2) I think, given the scientific basis available at this time, the risk is probably blown out of proportion in the arguing against RD; as for what can be said whilst claiming to be in lieu with available science, I find this quote agreeable;
(underscore added for emphasis)

If you did the same decompression time, but distributed your stop time shallower, then you would almost certainly have less risk, The actual difference in risk might be relatively small, and perhaps not worth arguing about. Nevertheless, if people seek the truth on the path to least risk for the same decompression time I very much doubt that RD2 is the answer!

How can you find the quote agreeable with the last part of Dr Mitchell's post that you quoted above?:

...Nevertheless, if people seek the truth on the path to least risk for the same decompression time I very much doubt that RD2 is the answer!

 

[Dan_P]

How can you find the quote agreeable with the last part of Dr Mitchell's post that you quoted above?:

Hi Ayisha,

That's a good question.
The reason I wouldn't contend a claim as to an ultimative answer to the decompression question, is three-fold;

1) Cardinally, I wouldn't assume a "standardized" paradigm to yield "optimal" results. If ever it did at all, I'd assume such cases to be rare - this I hold to be true for standard gases, and I hold it to be true for standardized decompression paradigms.
I personally accepted the suboptimal nature of such a paradigm, to gain other benefits.

2) I don't believe things to be black and white here - if there is an optimal algortihm, I would believe it to be a different one for me than you, and a different one for me today than tomorrow.

Ratio Deco is taught in a defragmented fashion. That is, you learn ratios at increasingly deeper set points.
Those are derivatives of Cascade Deco.
What's important is that the nature in which they're taught, is very open to personal adaptation throughout - that is, one of the points of teaching RD, is to get divers to engage in their decompression, and progressively develop their strategy.

3) There is scientific backing to assume a position that deep stops were probably overemphasised, at least in RD1.0.
I agree with that.

I don't see by how much, but the quote didn't make any claims in that regard.

I don't see definitive proof, but the quoted statement didn't make any claims in that regard.

When I react on this board, it's typically to much more ultimative and less carefully weighted statements, or attacks.

 

[tbone1004]

I'm not about computers failing. Absolutely, that can happen, but you'd need to go through a small armada of failures for that to be the probem, unless everybody in the team is using the same hardware/software. In either case, that's not within my range of motivations.
I'm about engaging decompression questions and choices, growing and adapting my approach as I develop, avoiding dependency on anyone or anything, staying athought continuously, and developing divers to do the same.
I don't have a problem with the use of computers, I just feel that ratio deco is also a good way to dive/develop and personally prefer that one by far, for the pros and cons that it has.

you mean following the teachings of the great AG who can do no wrong with his decompression approach. Despite being able to give off bubbles like a super hero, having been bent on his own algorithm, then paid for a study to be done which showed that not only was his approach less efficient than an outdated set of gradient factors, but also showed more signs of decompression stress?
Do you have a MD or PhD in a relevant field and are actively studying decompression stress? The guys that do say that the theory that you base your decompression on is not the best form of decompression, yet for some reason you think AG and by association, you are more qualified to determine decompression profiles than guys with terminal degrees in relevant fields who are actively studying the science and art of decompression? Please explain that one

 

[tbone1004]

It is not ridiculous, it can happen. When my gekko was in error it was just showing time, depth and temperature.

I did deco by myself that dive and also the next dive because my gekko was 48h in error.

I'm sure that has nothing to do with the fact that that computer is not designed to do decompression, is decades old technology that hasn't been updated, did exactly what it was designed to do, but you didn't read the manual to anticipate that it isn't a decompression computer.
Those types of computers are what GUE was talking about when they wrote the Bakers Dozen, not things like Shearwaters,Ratio, Divesoft, OSTC, etc.

 

[barth]

I'm sure that has nothing to do with the fact that that computer is not designed to do decompression, is decades old technology that hasn't been updated, did exactly what it was designed to do, but you didn't read the manual to anticipate that it isn't a decompression computer.
Those types of computers are what GUE was talking about when they wrote the Bakers Dozen, not things like Shearwaters,Ratio, Divesoft, OSTC, etc.

I thought the same thing was possible for a VR3. I thought that is was possible for a VR3 to give a message "use tables". I think that computer was designed for techdiving.

How do you know something like that can't happen by Shearwaters,Ratio, Divesoft, OSTC, etc. ? ;-)