What makes us think we can trust any of them

[Potapko]

I had hoped this would not turn into another computer vs brain thread. There certainly enough of them on here. Calculating simple max bottom time from a table and then diving according to that is a no brainer. No better than leaning on the computer imo. However, with every, read most, divers goal being to remain at depth as long as possible (safely), Using the most liberal computer to calculate multilevel changes will give the longest run times. If there is no greater danger than with a more conservative comp, because nobody really knows how their body will react anyway, why not use the liberal algorythm for calculations?

 

[halocline]

There is no evidence that liberal computers are more dangerous than conservative ones, as I posted before. People buy conservative computers because they feel safer with them, as it is intuitive to believe that a more conservative algorithm will be more effective at preventing DCS than a liberal one. But that doesn't make it factual.

I suspect some day there will be enough of a data pool to do a study to determine if there is any colloration between algorithms and DCS prevention in recreational diving. If that happens, I hope I don't have stock in whatever computer manufacturer is found to use a "less safe" algorithm! Until then, you can also take some solace in the fact that the computer companies are probably REALLY skittish about getting sued, and do everything they can to make sure their software is as safe as the next guys'.

 

[WarmWaterDiver]

I don't see this as a computer vs. brain thread - I see this as a DCS avoidance thread. But your title using the worjd "trust" and "them" with a link to a magazine article on dive computers lead me to think you were interested to know which could be absolutely trusted. The answer is none. However, there should be statistical data available to show probabilities one one algorithm vs. another - but I have yet to see that data publicly posted anywhere (not just this thread or board).

There is an article you may find interesting in a UK diving magazine titled "Which DoYou Trust" and the emphasis is on "You" for personal choice, rather than "We" in your title, for more than one invidual to choose to "Trust".

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

This topic of different algorithms yielding different results is not quite new - here's the earlier dated article in the UK magazine on comparisons - it's from 1995 - 10 years ago now. There are more algorithms to test and compare against now though (RGBM wasn't a dive computer algorithm in use at that time in the article for example).

http://www.divernet.com/gear/comps995.htm

The last four sentences in thaat 1995 article still hold true today. There are no commercially available dive computers monitoring users' body conditions directly. That article also uses the word "you" in similar context to the 2003 article.

Different automobile manufacturers post things like braking distance on the various models manufactured as an analogy, but I don't necessarily "trust" those figures in light of tire wear, driver skill, road conditions, etc. all being important variables that aren't absolutes. I haven't seen an article on an auto accident where someone was declared to not be at fault because their vehicle didn't stop within the published braking distance. It's the individual operator and choices made that are the key.

For dive computers and liability, I think far more weight is put on the verbiage in the owners' manual than in comparison against competitiors' algorithms.

 

[Uncle Pug]

I had hoped this would not turn into another computer vs brain thread.

Because we have new readers we need reiterations of the old answers to new threads that pose the same old questions.

It really isn't about computers vs brains... or even computers vs tables vs brains...

What Snowbear brought to the thread is just common sense: slow your ascent more and more the closer you get to the surface and you will feel better while at the same time maximizing your underwater experience.

most divers goal being to remain at depth as long as possible (safely)

Thinking in terms of maximizing the dive rather than just staying at depth as long as possible greatly increases safety and also allows one to experience different levels of the dive.

It really isn't complicated. Just shape your dive curve right and spend time enjoying the shallow portion of the dive.

Oh, and to answer your openning question: Personally, I wouldn't.

 

[colby]

When I took my OW course, we dealt with tables. And this statement may be oversimplifying, but he said that we will probably be diving at some point in time with computers, but computers may fail, so always backup the computer dive with a table calculation because that will be the most conservative of all.

 

[Diver0001]

After reading this article: http://www.scubadiving.com/gear/dive_computers/crunching_the_numbers/0/

I begin to understand why the DIR folks keep telling people not to dive according to their computer. The difference in remaining ndl time between the tested computers on a given profile was as great as 66 minutes. That's nuts!

Not really. The Genesis computer tested has one of the oldest algorithms on the market and should be seen as the baseline for teh worst case scenario. The Citizen isn't even on the same page with the rest and would be considered by most to be basically experimental in it's approach and the rest of them are in the same bandwidth.

The computer is a model (just like the 120 rule, ratio deco and all that other kool-aid guzzling mumbo-jumbo) and you need to apply some intelligence to (a) understanding the model and (b) understanding the thinking behind the model. Once you've done that it doesn't matter so much what the model says. It just gives you a handle. Your innate human ability to understand and process the *rest* of the information that the model ignores will fill in the rest.

Computers don't rot your brain. Your brain will rot just fine without them. Your responsibility as a diver is to make sure that both the computer (even if it's in table form) *and* the brain are engaged.

R..

 

[Web Monkey]

It's not always that simple, since some computers are more liberal than some tables, as well as the other way around.

Also, if you're diving with a computer, you should still know how to use tables, however if you're diving a multi-level profile, it's going to be very difficult to use tables as "a backup" for that particular dive, unless you have detailed information about your dive profile.

FWIW, the "What if your computer breaks during the dive?" problem isn't actually a very common occurance, and as long as you're diving within the "No Decompression Limits", what actually happens is that you notice your computer is hosed, do a nice slow ascent, a safety stop and end the dive.

Even without hard numbers, you still need to know enough about the tables to have an idea when your computer has lost it's mind, when to take it's advice and when to ignore it. For example, after a relatively shallow 45 minute nitrox dive, my buddy's computer told her she had something like a 15 minute decompression obligation, which was clearly insane.

Also, the flip side of "computers may fail" is that "people may fail". There's a risk on both sides. It's certainly easy enough to lose track of what group you're in while flipping over a dive table, just as it's possible for a computer to fail. In either case, you need to have a good idea what's reasonable, so you can tell when something is wrong.

Terry

When I took my OW course, we dealt with tables. And this statement may be oversimplifying, but he said that we will probably be diving at some point in time with computers, but computers may fail, so always backup the computer dive with a table calculation because that will be the most conservative of all.

 

[Snowbear]

Calculating simple max bottom time from a table and then diving according to that is a no brainer. No better than leaning on the computer imo.

I totally agree with you here. No brains needed for either.

However, with every, read most, divers goal being to remain at depth as long as possible (safely)...

Well, sort of. As Pug pointed out - many divers are learning to make the most of the entire dive, not just the deepest part(s). Even in Palau, when most divers were maximizing their time at 40 or 50', several of us (OK - mostly just me ) were spending more time on the shallower parts of the reef.

Using the most liberal computer to calculate multilevel changes will give the longest run times.

Not really. I have found that I can almost always get longer run times than most folks' most liberal computers. And I leave the water feeling way better than I ever did in the days when I was following my very conservative Suunto.

... because nobody really knows how their body will react anyway, why not use the liberal algorythm for calculations?

I disagree with this as well. True I cannot know that I may get bent doing the profiles I do, but as I've stated so many times before, my body likes the way I'm shaping my dive curves a whole lot better than how the Suunto shaped them

 

[Charlie99]

Using the most liberal computer to calculate multilevel changes will give the longest run times.

Not really. I have found that I can almost always get longer run times than most folks' most liberal computers.

Please clarify this. Are you saying that a liberal computer will still show required deco when you exit the water after following your preferred profile?

my body likes the way I'm shaping my dive curves a whole lot better than how the Suunto shaped them

I was unaware that the Suunto or any other computer limited you to a particular shape of dive profile. Please explain what you mean by "how Suunto shaped them".

 

[Snowbear]

Please clarify this. Are you saying that a liberal computer will still show required deco when you exit the water after following your preferred profile?

Nope, I am saying even the most conservative computer will have long since "cleared" when I exit the water.

I was unaware that the Suunto or any other computer limited you to a particular shape of dive profile. Please explain what you mean by "how Suunto shaped them".

I'm talking about how *most* folks use a computer.... and like I pretty much used to.... by either not letting the "NDL" number turn into a "deco required" number or by not letting the little bars get into the "red." I would base my bottom time on what was "allowed" by the computer. Like most, it would grant me more NDL time for multi-level profiles. As long as I kept my ascent rate under 30fpm, all I had to do was the 3 minute "safety stop" anywhere between 20' and 10' (I would always try to keep it above 15' and below 10'), then I would ascend to the surface. This ascent would usually take about 30 seconds, which is generally considered pretty slow.
As for the curve that was shaped, they typically looked like the first thumbnail.
My profiles these days look more like the second one...