The old tables vs computer argument

[Thalassamania]

The fact that one is a professional table cutter doesn't mean one therefore inherently knows the rules of RD. That's just silly. What it does mean is that Hamilton is a very good person to ask about how well the schedules RD generates match against decompression theories, but one first has to know what schedules RD actually generates (and that does have to be learned, even by a "professional"). How else could one judge the validity of the curve fitting? You have to know what curves are being generated. As for RD, that depends entirely on how you define the rules (which standard gases, for what exposures, for what depths, for what conservatism, for what other assumptions, etc). These all have to be defined by someone. They are not some sort of universal givens. Hamilton cannot deduce what rules GUE/AG have defined based on any sort of first principles or understanding of decompression theory. They aren't one and the same. I don't know how else to make that clear.

Andrew invited me to sit in on his web course, I guess I'll do so and report back.

Again, I have to disagree that it's not tested.

OK, please supply me with the reference for the learned peer reviewed journal(s) in which the trials were reported.

If I have a bag of M&Ms, all of which have been tested an approved as safe by the FDA, and I choose to only eat the green ones, I'm still eating something that has been tested.

That's as close an analog as my brain is willing to provide at 6:40a.

Not close enough for me to understand you point.

(I'm possibly wrong, but I'm not really expressing myself well)

I believe that you are, if you'd like to try again, that'd be fine.

I am in complete agreement that if you are doing a new dive, one that is dramatically different than others you've successfully completed, by all means run them through the software to ensure that your profile is in the ballpark.

If you have to do that what use is it, except perhaps as an emergency response to having to alter the plan on the fly?

But do you know whether the FDA approved the green M&M's because they knew that they would only exist as a percentage of total M&M's?

Do you know whether 100% green M&M's was tested?

Before someone accepts test results, they should try to find out what was tested and how. Then they can try to fit there problems to the results of tests.

Richard

Point well taken.

 

[boulderjohn]

I am coming to this discussion as someone who studied deco theory fairly intensely before even looking at RD. I am now studying the theory behind RD. (Yes, I am a UTD student right now.) For a variety of reasons, I don't want to go too much farther into this than has already happened, but I do want to step in on a couple of issues.

You're always free to check the RD profile against software. It's actually what GUE encourages. Once you realize that the profiles you typically dive match up exceedingly well, the flexibility of RD becomes a huge plus.

My introduction to RD came when a Gue-trained diver saw a V-Planner created deco profile, said, "Hmm, that's not right," and used his RD training to create something very different. I did a lot of investigating after that, and I am still investigating. I have talked directly with many key people about this issue, including Andrew Georgitsis. I assure you that RD, at last as far as UTD teaches it, will not always match up with popular deco planning software, and as far as I can tell, Andrew is not the least concerned about that.

Again, I have to disagree that it's not tested.
...
Ratio Deco is a gross simplification of decoplanner inputs (i.e. only a few gases), and observation about what schedules it produces with both Buhlmann and VPM algorithms using that reduced input set.

It's no less tested than the algorithms upon which it is derived, and between the two of them that represents the vast majority of empirical evidence out there.

I am pretty sure DecoPlanner has never been tested. Part of my research included discussions with Gene Hobbs of Rubicon, who told me neither RD nor DecoPlanner had been tested. He gave me access to what he thought was the best information at the time, some of which was not yet published. I saw nothing related to DecoPlanner.

 

[Rainer]

Seeing as DP includes straight Buhlmann (you can add GF) and VPM, it's as untested as those very models. As for "testing" RD, to me it's the equivalent of "testing" the Rule of 120. Neither is a decompression theory, so all you're testing is how well the schedules match. You don't need a peer reviewed journal article for that. You simply need to be able to read graphs.

Oh, and if you don't think the run times of RD match very close to V-Planner +2, I'd suggest playing around more with both (for T1 dives, they're basically always within a minute of each other). The shapes of the curves certainly are not identical, but that's due to other factors (mostly s-shaping for O2-window effects, which IS something that could use plenty more research!).

 

[boulderjohn]

Oh, and if you don't think the run times of RD match very close to V-Planner +2, I'd suggest playing around more with both (for T1 dives, they're basically always within a minute of each other). The shapes of the curves certainly are not identical, but that's due to other factors (mostly s-shaping for O2-window effects, which IS something that could use plenty more research!).

I did not say run times were different. It was indeed the curve I was talking about.

...and O2 window effect does seem to be the key factor in that, doesn't it? I have done quite a bit of reading on topic, and I guess I am still waiting for the research you are awaiting yourself.

There was a very good thread on that a while ago in the Ask Dr. Deco forum.

 

[Rainer]

Thanks, I'll take a look for it.

 

[Nemrod]

Many people of every generation have a problem acception new things. Like a home computer for instance. When the desktop PC was becoming popular I just didn't see the importance or the value of them. Changed my mind though when Windows 98 came out. Another instance is the electric starter on a Harley. I thought that only sissies would use a button to start one. After about twenty years of cranking, hurting my ankle and cussing because I didn't get the gas/air mixture right I gave up and got one. Never be without either one now. I've only dived with a computer and never learned the tables. It's going to stay that way.

You should know the tables for the day that will come when your computer gives out that error message, Windows Subscription Expired. Garbage in and garbage out. Knowing the tables allows the computer diver to evaluate the validity of what his computer is telling him and to complete a dive safely when it fails. Oh, you carry two to cross check, ok, which one is right? Your brain is a computer, the best ever made.

N

 

[boulderjohn]

Thanks, I'll take a look for it.

Here it is:

http://www.scubaboard.com/forums/ask-dr-decompression/224754-oxygen-window-explanation-purpose.html

 

[boulderjohn]

Mark Powell (Deco for Divers)gives three different definitions commonly used for the term oxygen window.

Here is what he says on page 58:

So what advantage does the oxygen window give us? Well one thing it doesn't do is that it doesn't help us to off-gas any quicker. The rate of off-gassing is dependent only on the individual inert gas gradient, in other words gases off-gas at the same rate no matter what the other gases are doing. So the fact that the Oxygen partial pressure is lower on the venous side has absolutely no impact on the rate that Nitrogen (or any other inert gas) off-gases.

(Note: I corrected the spelling in the quotation but not the punctuation. The book is a really valuable resource for deco theory, but Mark needed a better editor.)

 

[Trace Malinowski]

While the methods employed by the DIR community may be in the minority at the moment, it doesn't mean that those methods will always be in the minority. The only way to effect change is to develop a stronger voice. Had minority racial groups never taken a stand against the status quo in the United States, President Obama would not be in the White House today. Our country is better for the efforts of the first black men and women who faced the impossible odds of their time for equality. There are still miles to go on the march toward racial harmony, but every person who contributes to the dream takes us one step closer.

While that cause is far for noble and magnificent than tackling the current issues of the diving industry, it demonstrates that silence and servitude accomplishes nothing. When asked to leave a dive center for having double tanks and a depth gauge and timer, I felt the closest thing to being discriminated against as a white male. It was incredulous to me that, despite a volumous stack of C-cards from respected organizations, my buddy and I were told we were dangerous and we wouldn't be back on the boat in time. What time do you want me back in the boat? Yesterday, I was only 20 seconds behind my planned ascent time. Do you want me to go right back down? I can do that with ratio deco too. I can be back as soon or as late as you like on my next dive.

This is BASIC SCUBA, but PADI does not control the diving industry and for two agencies and many instructors, this is "basic scuba" taught to recreational open water divers. One day, more divers than we know will be diving differently than today. Maybe DIR, maybe something better.

Been diving. Thal and Doc, I'll reply to PM's shortly.

As agreed, it does produce a very conservative dive profile... problem is, that level of conservative diving is not always available to the average diver. Bluntly, many could not use it, even if they wanted to.

Remember, we are in "basic scuba".

You get on a boat going out diving... the boat plans to go to a specific site.. but when they get there, someone is already there, the wind is blowing the wrong direction.. something stops them.. so they go to another site...this one is deeper...you now make your dive.. with say 33% nitrox to around 90 ft....but they used up time going to this new site, so you want the maximum bottom time, and they want to get back for the afternoon run...which leaves a problem.. you can take longer, but your surface interval will be shorter.. or you can dive shorter and have that one hour (but no longer) surface interval. I choose to have the longer dive, with a shorter surface interval...your system does not allow that.

Situation two.. you are a spear fisherman... you see a really large fish and shoot it.. but you get into a major physical battle...you loose track of how deep you got.. you are worn out...what to do now? The computer actually knows that you have been working and greatly reduced your NDL, so you don't add a chamber ride to being tired.

Note: Increased circulation increases your nitrogen absorption.. several laws of physics involved here, backed up by actual bubble measurements...

Your system hopes that it so conservative that you cover this event.. computers can actually adjust for it.

You plan a dive for say 80 degree water, but when you actually do the dive, the temperature at the bottom is 74 (that actually happen last July in the northern gulf)..suddenly, your three mil is not so warm...

The computers can be made to adjust for sudden, unexpected changes in a way that doing math in your head cannot. However, if you have lots of time, are on no schedule, it still works well. Trouble is, that is not the majority of the diving being done..

And diving very conservatively ends up meaning a lot of missed bottom time and lost dives.

I don't think anyone want to get a case of DCS (at least I hope not), but doing every dive with a huge extra safety margin over what is already hugely safe, does not work that well in a lot of places.

Nor are the majority of divers ever going to be doing team diving...nothing wrong with it, just that it will never be more than a small percentage of people.

 

[Rhone Man]

While the methods employed by the DIR community may be in the minority at the moment, it doesn't mean that those methods will always be in the minority.

You may be right, but personally I don't see the "just say no to computers" thing ever catching on. Off topic, but I'd also be surprised if the trimix from 100 feet thing catches on.

DIR has a lot to offer the diving community as a whole, but some aspects of it vary between positively quirky and downright Luddite.