Grrrrr.

[peter k]

Here's a well thought out response to 'pooters;
(C'n'Peed from a.n. other forum)

In 1995, when my first article with this title was published, I cited the two major reasons behind my argument were that dive computers encourage divers to skip some vital aspects of dive planning; and, in any event, dive computers twist the decompression algorithm so badly that they were conservative to the point of being potentially dangerous.

That first article didn’t cause much of a stir, just a few emails and phone calls from divers who thought my ideas were crazy and a marketing letter from an equipment manufacturer offering me their latest dive computer as a demo!

It’s true that the functions and features of dive computers have progressed considerably since the mid-90s. It really seems from today’s vantage point that we were back in the stone ages then. Now there are models that manage multiple gases for decompression, figure helium bottom mixes into the calculations, and some that use bubble model algorithms like VPM.

However, with eight years more experience teaching and diving, the arguments against using computers for technical diving remain the same and are as strong as ever.

Let’s recap the major challenges: Divers seem to use computers primarily because they don’t have to plan their decompression schedule: the computer does it for them. This may sound wonderful. But think about what this means in a dive involving multiple stops and multiple gas switches… The diver has little or no way to play with “what if” type scenarios nor can she easily look at the impact of something like a late or early gas switch, using a second or third decompression gas or dropping the PO2 in her bottom mix to better manage CNS stress.

In fact, when you look at it from that perspective, by using a computer, she has just handed over responsibility for DCS planning and CNS risk management to her computer. She will gain zero experience in both these areas by using a computer. This dependence on a “quick fix solution” – especially in the case of less experienced technical divers – discourages the necessary fundamental understanding of decompression theory and gas management.

I think the “training and understanding” issues are pretty compelling, but there is one even more grave shortcoming that we need to get out in the open. But before we move on to that, there are a couple of other small points. Dive computers are expensive. I see people with two or three of them! That’s a trip to Truk Lagoon right there. Computer manufacturers also seem to have lost touch with their customer base and what they want and need from computers. Seems to me the screens are getting smaller, but there’s more and more information crammed into the available real estate. And most of the information on-screen is totally irrelevant – for instance, do you really need blinking notification that your CNS level is at 3% in lieu of notification that your depth right now is 210 feet?

OK. Now we will look at the big issue.

Computers twist the algorithm to a point that it will create a padded decompression obligation. Often that padding will be an obscene distortion of the algorithm. With an uneducated diver who got into staged decompression by accident, this might be a bonus, but for someone trained in decompression theory and someone who understands the vagaries of decompression planning, spitting out a decompression schedule with training wheels attached is ridiculous. And is potentially dangerous.

I have my own theory as to why this is and it really has to do with risk management. Unfortunately, rather than managing the diver’s exposure to risks like DCS and CNS toxicity, it’s about limiting the computer company’s risk in court!

Most dive computers – all the ones I’ve seen -- come with warnings that we should not use them for decompression diving. This is a little strange since quite often the instructions that are packaged with computers talk about how those computers handle decompression diving. Anyway, what those instructions do not explain is that the manufacturer’s legal department have twisted things so that if you should sue them, they can point out to a jury that: “Our computers are designed to keep divers in the water 50% longer than the standard algorithm recommends.” Since the jury will not be divers, it only remains for the company’s lawyers to roll out “an expert” to explain to them that if 10 minutes of deco is called for, then 15 minutes MUST be better! There is no consideration given for thermal stress, gas management, CNS toxicity.

In short, this simplistic view of the world of technical diving doesn’t work too well where I do most of my diving and teaching – which is in North America’s huge inland fresh water seas, and among the best wreck diving in the world.

To be fair, computers do have a place in my world… usually at the end of a line in about 20 feet of water clearing while the rest of the team, sits drinking Gatorade and watching video from the dive

My advice, get a digital bottom timer, buy a copy of V-planner for your PC and learn the face of the algorithm so you can plan your dives properly.

Take care, and Dive Smart.

Peter

[Mark Chase]

Unfortunatly the well thought out responce is out of date at best or wrong at worst.

Originally Posted by [b

Quote[/b] ] In 1995, when my first article with this title was published, I cited the two major reasons behind my argument were that dive computers encourage divers to skip some vital aspects of dive planning

Thats the divers fault and nothing to do with the computer. Any diver who does a decompresion dive without planning it first is asking for trouble.

Originally Posted by [b

Quote[/b] ]Divers seem to use computers primarily because they don't have to plan their decompression schedule: the computer does it for them. This may sound wonderful. But think about what this means in a dive involving multiple stops and multiple gas switches. The diver has little or no way to play with & what if? type scenarios nor can she easily look at the impact of something like a late or early gas switch, using a second or third decompression gas or dropping the PO2 in her bottom mix to better manage CNS stress.

All of the above can be done on the VR3, I can reprogram gas mixes in the water, ditch travel or deco gas and recompute the profile, fly the curve and make the deco more or less agresive as I wish and I can use up to 10 gas switches in my dive profile with 4 pre programed profile options.

Even my humble Vytec would allow ditching of the deco or travel gas and would recompute time to surface as required on the remaining gas.

The Vytec would not allow a gas switch above 1.6pp02 and would prompt a gas switch if you forgot. If you switched late the computer would recompute your profile. I would like to see a table do that.

Most computers allow dive planning usualy on a PC prior to the dive and all the necessary gas issues can be explored at that time. The VR3 has a deck top package which exactly mirrors the wrist computer and you can pre plan the dive to cover allmost all variants and see what he wrist computer will tell you during the dive.

Originally Posted by [b

Quote[/b] ]This dependence on a quick fix solution, especially in the case of less experienced technical divers discourages the necessary fundamental understanding of decompression theory and gas management.

Again thats the divers problem dont blame the computer. Almost all tec divers use a desk top computer to plan their dives so whats the diferance?

Originally Posted by [b

Quote[/b] ]Dive computers are expensive. I see people with two or three of them!

So is trimix. OK lets all do deep air. Two or three computers. Ahhhh a good safe diver carrying a redundant computer and possably a bottom timer and depth gauge for bail out. Dive kit is expensive. A computer costs no more than a BCD or a Twin set or a good set of regs.

Originally Posted by [b

Quote[/b] ]Seems to me the screens are getting smaller, but theres more and more information crammed into the available real estate. And most of the information on-screen is totally irrelevant, for instance, do you really need blinking notification that your CNS level is at 3% in lieu of notification that your depth right now is 210 feet?

OK so he baught the wrong computer. Get a big one not a fancy sudo wrist watch. None of my computers blinks a CNS warning untill it hits 80%

Originally Posted by [b

Quote[/b] ]OK. Now we will look at the big issue.

Computers twist the algorithm to a point that it will create a padded decompression obligation. Often that padding will be an obscene distortion of the algorithm. With an uneducated diver who got into staged decompression by accident, this might be a bonus, but for someone trained in decompression theory and someone who understands the vagaries of decompression planning, spitting out a decompression schedule with training wheels attached is ridiculous. And is potentially dangerous.

Why is this a big issue? Its the tierd old argument that tables will get you out of the water quicker than a computer. This of course is total rubbish. A fast computer on a low safety setting will get you out of the water faster than a slow conservitave pre cut table. A streight Bhulman 100/100 table will get you out of the water quicker than most computers but is very agresive and likley to bend in UK conditions and a less than 100% fit and well prepaired diver.

I dive tables and a computer and I can tell you from experiance that the computer will invairably get you out of the water quicker than tables. This is not because the computer is more agresive it is because the dive is table planned on a square profile often deeper than the actual multylevel dive.

Typicly a dive like 45min at 50m on the Moldava ends up as 25min at 48 and 20mins at 45. but as its a big wreck you never quite know your profile till your actualy on the dive.

The other BIG issue is not an issue. NO ONE should atempt a decompresion dive without proper training. Once trained the computer is a valuble TOOL. It is not a total brain replacement and should not be acused of being dangerous. Its like the gun analargy. A gun never killed any one it was the person who pulled the triger that did that.

Originally Posted by [b

Quote[/b] ]Most dive computers & all the ones Ive seen -- come with warnings that we should not use them for decompression diving. This is a little strange since quite often the instructions that are packaged with computers talk about how those computers handle decompression diving

My Vytec is sold as a full decompresion computer and so is my VR3. This demonstrates how out of date this artical is. Most modern computers cope with deco. If they say they dont then dont use them. Simple. The ones (Like my old Mares Surveyour) that say they dont, will offer a deco profile as an emergancy back up but they do not pretend to be full decompresion computers. Obviously the manual explains how to use the emergancy system but it offeres loads of warnings stating that this should not be considered useful for general diving.

Originally Posted by [b

Quote[/b] ]Our computers are designed to keep divers in the water 50% longer than the standard algorithm recommends. Since the jury will not be divers, it only remains for the companys lawyers to roll out an expert to explain to them that if 10 minutes of deco is called for, then 15 minutes MUST be better! There is no consideration given for thermal stress, gas management, CNS toxicity.

I have never had any compouter show 50% extra deco compaired to my tables? Thermal considerations are the pre planning responsibuility of the diver. CNS tox is not an issue for divers unless they are exceeding guidlines for bottom gas and gas switching. I had to do a 70m dive with 40min bottom time and three gas switches before I hit 100cns+ on a dive and then a simple drop to 80% for deco reduced this to 69%. Some one atempting this type of dive without the proper planning and training is a Darwin experiment thats about to go wrong.

Originally Posted by [b

Quote[/b] ]In short, this simplistic view of the world of technical diving doesnt work too well where I do most of my diving and teaching which is in North Americas huge inland fresh water seas, and among the best wreck diving in the world.

Whats the betting he uses a VR3 now? Bearing in mind it wasent invented untill 2000 this artical was probably writen before he was aware of its existance.

Team Delta (one of the leading deep mix groups in the UK) all used tables and bottom timers. Then my m8 Pete shows up with a VR3. They all got fed up with him getting out of the water safe and unbent before them so now they all dive VR3's


Thats progress

ATB

Mark Chase

[Mdemon]

Er... what Chasey said.  Eloquently put, Mark!

My 2p's worth - computers manage millions of calculations per second regardless of depth, Po2, Nitrogen, beer the night before or unexected variations in the dive plan.  Divers struggle with one.  And they have plenty of other things to worry about/enjoy than doing maths and playing with tables.  Knowing how to use tables and having them as a backup is fine, but we should be playing to strengths, not weaknesses - let the computer do the hard work.

[Bob Cooper]

I've got a computer! I use it at work and for sending e-mail and for participating in bulletin boards etc.  I also use it for dive planning (my buddies send me e-mails which tell me what time the boat leaves and which gasses we will be using).

Apart from that, I don't want any kind of computer strapped to my wrist during my dives.  I use my little tables written in my wetnotes.  The only usefulness I find is having a Vyper which I can download to my PC to see my dive profile.  I usually look at this and think to myself "why did I do all thay deco!"

Bob (tounge in cheek)

[Mdemon]

Hey, I got a Vyper too!  The graph function is good - a great reminder of the dive.

My gripe with computers is a) they refresh too slowly - I'd like real-time depth, not every few seconds and b) the functionality is very limited.  Why can't we upgrade the software from the PC like you can with GPS (OK, you can with the VR3 I believe).  And why no games (yes, I know, the VR3 does...) or downloadable pictures/text so you can have something to read during deco?  And why can't I have a voice telling me useful stuff, rather than incomprehensible beeps???  And why not show the profile on the screen so I can make a judgement about how agressive I can be on the deco?

Right.  Got that off my chest...  Any Suunto developers on here?

[Mdemon]

Hey, I got a Vyper too!  The graph function is good - a great reminder of the dive.

My gripe with computers is a) they refresh too slowly - I'd like real-time depth, not every few seconds and b) the functionality is very limited.  Why can't we upgrade the software from the PC like you can with GPS (OK, you can with the VR3 I believe).  And why no games (yes, I know, the VR3 does...) or downloadable pictures/text so you can have something to read during deco?  And why can't I have a voice telling me useful stuff, rather than incomprehensible beeps???  And why not show the profile on the screen so I can make a judgement about how agressive I can be on the deco?

Right.  Got that off my chest...  Any Suunto developers on here?

[Mark Chase]

Originally Posted by [b

Quote[/b] (Mdemon @ Oct. 21 2003,22:33)] 

Originally Posted by [b

Quote[/b] ]Hey, I got a Vyper too!  The graph function is good - a great reminder of the dive.

The VR3 one is crap. I use my Vytec.

Originally Posted by [b

Quote[/b] ]or downloadable pictures/text so you can have something to read during deco?

The VR3 is offering downloadable books as an upgrade and persolised visuals / downloadable images on screen

Originally Posted by [b

Quote[/b] ]And why not show the profile on the screen so I can make a judgement about how agressive I can be on the deco?

The VR3 shows the deco graph on screen and also shows the deco GF as a man climbing a rope into a box. You can fly the curve by folowing the position of the man on the rope.

Originally Posted by [b

Quote[/b] ] And why can't I have a voice telling me useful stuff, rather than incomprehensible beeps???  

OK you got me there

ATB

Mark Chase

[Mdemon]

Dammit!  Sounds like I need a VR3!!!

I wonder if there is an SDK, a kit which allows you to program it?  I could have some fun with that...

Can't really justify the cost at the moment though - might be cheaper to waterproof a PDA.  Mind you, old laptops are so cheap now, might as well waterproof one of them.  Then I could watch dvd's on deco...  A diving first?