drop some knowledge on me: algorithms

[ThatsSomeBadHatHarry]

I've been looking around the forums and i cant seem to find basic info on algorithms. I know the purpose of an algorithm (sort of) but how one computer can use a more conservative algorithm than another and still be trustworthy escapes me. how can liberalness vs conservativeness help me out in each's respect? i dont know, just tell me something so i can sleep at night.

 

[MoonWrasse]

You can still get bent using either conservative or less conservative computers. Remember none actually tell you what's going on in your body, nor will they automatically factor in contributers such as age, fitness, dehydration, booze, fatigue, etc.

 

[TSandM]

A simple answer to one of your questions: A liberal algorithm gives you more bottom time at a given depth; a conservative algorithm should give you a bigger safety margin (decreased DCS risk). In practice, it is difficult to see a significant safety difference among the commonly used algorithms (or tables) because the use of any of them has decreased the DCS risk to such a low level.

What is important to realize is that all of the tables and computers in common use are attempts at mathematically modelling a process which is not truly and completely understood. The different algorithms utilize different assumptions about gas dynamics within the body -- some just look at dissolved gas, others take bubble behavior into consideration. Some assume that gas loading is serial (one tissue after another), at least one assumes it is parallel. Nobody can do actual nitrogen monitoring of various tissues during diving, so all of this is fairly theoretical, and validated to different degrees by animal studies or by divers who nowadays are subjected to doppler monitoring for intravascular bubbles.

The big advance was Haldane's original observation about the 2:1 ratio (actually 1.58:1) that was tolerated before animals became symptomatic from DCS. Everything since then has been attempts at refining the model, but the biggest decrease in risk came with the initial insight. Nowadays, DCS persists as a sporadic event even in people who dive well within conservative parameters, but the incidence is low.

What you use depends on your risk tolerance/aversion.

 

[WarmWaterDiver]

There are some decent write-ups on relative differences between commonly used algortihms, if that's what you're actually looking for. Here's one from a few years ago on "Which do you trust?" with the emphasis on YOU

http://www.divernet.com/equipment/computers2003/intro.shtml

And, here's one of the latest

http://www.divernet.com/equipment/0306compsextra.shtml

From this side of the pond, these are reasonably recent.

http://dive.scubadiving.com/images/200408GR_computer_charts.gif
http://www.scubadiving.com/gear/dive_computers/crunching_the_numbers

And this article's title is "Liberal vs. Conservative"
http://dive.scubadiving.com/PDF/200505_divecomps_graphs_01.pdf
http://www.scubadiving.com/gear/dive_computers/smart,_sleek_and_sexy

 

[mozz]

bad hat harry,

think of it as the difference between buying a volvo vs. another sedan. either vehicle will get you to your destination. however, it is comforting to know that the added safety features built into the volvo are there when you need them. also true is the fact that if you are a safe driver, all vehicles are safer. enough of the simplistic analogies. TSandM gave a wonderfully articulate overview of the dynamic of your question. suffice it to say that there are different models and be aware of what their parameters and limits are. ultimately the decision to use one or the other should be based on your educated opinion. good luck and be safe.

 

[wedivebc]

This Dr I know who used to work for DCIEM told me "divers think deco tables are like threading a needle, it's more like driving a Volkswagen into a barn"
They just aren't that finely tuned. It is a predictabilty thing. Most people don't get bent if they follow a cretain ascent curve, but some will no matter what.

 

[Diver0001]

how one computer can use a more conservative algorithm than another and still be trustworthy escapes me.

You've put your finger on it. Either an algorithm gives you adequate off-gassing <<for your body>> or it doesn't.

how can liberalness vs conservativeness help me out in each's respect? i dont know, just tell me something so i can sleep at night.

It can't. Every person's body is different and even one person's body is different from day to day. The line between bent and not bent is not black and white. There are degrees of risk depending on how far you go into the "gray" area that we don't know enough about yet. Liberal computers go further into the gray. Conservative computers still go into the the gray too but not by as much.

If you want advice then buy the most conservative computer you can find and then dive it intelligently. None of the models out there are 100% so you should be suspicious of any information the computer is giving you. If you assume that your computer is always lying and trying to hurt you then you're in the right frame of mind.

R..

 

[Double_D]

There is one method of preventing DCS that's 99.99% safe: Stay on the beach.

You can also use the big dive computer already installed in your cranium, a watch and the RDP and be just fine. However I'm guessing that, by virtue of you asking the question, you're already shopping for the new hotness.

At the risk of turning the already well summarized answer in this thread a new direction, I'd recommend you discuss your concerns with your LDS when purchasing your dive computer. Most have adjustable parameters so you can tailor your risk versus your dive profile. They can help you sort out which one's features are best suited to your particular needs.

There are dozens of threads you can search for on here discussing whose dive computer sent them to the surface way before their buddy's, etc. The author's concern is generally more bottom time instead of less risk. I still recommend you read them - sometimes the best way to answer your question is to look at it from someone else's perspective.

Good luck and safe dives!

 

[WarmWaterDiver]

There is one method of preventing DCS that's 99.99% safe: Stay on the beach.

You can also use the big dive computer already installed in your cranium, a watch and the RDP and be just fine. However I'm guessing that, by virtue of you asking the question, you're already shopping for the new hotness.

At the risk of turning the already well summarized answer in this thread a new direction, I'd recommend you discuss your concerns with your LDS when purchasing your dive computer. Most have adjustable parameters so you can tailor your risk versus your dive profile. They can help you sort out which one's features are best suited to your particular needs.

There are dozens of threads you can search for on here discussing whose dive computer sent them to the surface way before their buddy's, etc. The author's concern is generally more bottom time instead of less risk. I still recommend you read them - sometimes the best way to answer your question is to look at it from someone else's perspective.

Good luck and safe dives!

Last I knew, "undeserved hits" could still occur from this method as well. When did using the RDP become DCS risk free?

The DAN data showed the square profile dives to have the highest incidence of DCS in the Undercurrent article right about this time last year.

"Trustworthy" is still an individually definable term. Driving in Houston freeway traffic for example is never 100% trustworthy, but neither is driving within 10 blocks of one's own home according to insurance statistics.

 

[ThatsSomeBadHatHarry]

"Trustworthy" is still an individually definable term. Driving in Houston freeway traffic for example is never 100% trustworthy, but neither is driving within 10 blocks of one's own home according to insurance statistics.

i think you know what i mean by "trustworthy". that (above) is not it.