Inexpensive but not going to get me bent?

[*Floater*]

Some more stats for you:

1. DAN America data shows that around 72% of bent divers were using computers

2. DAN America data from 1997 indicates that 93.7% of such cases were diving within the limits of their computer!!

Very interesting data. Maybe someone here with access to DAN's stats could look into the following:

1. Does "diving within the limits of their computer" include not violating the ascent rates?
2. More recent data. (8 years is a long time)
3. Breakdown of that 72% figure by computer brand or algorithm - though the figure should be adjusted to control for how many of total divers use the brand or algorithm.

It would be very interesting to see the results.

For me the conservative computers are too conservative because very few people using liberal computers have complained about undeserved bends. Also you can always dive a liberal computer more conservatively, but not the otherway around, so they are just more flexible.

 

[halocline]

If there are no stats on this issue (at least that we aware of) then it is not possible to state "the stats simply don't support that claim". Non-existent stats can't be used to either support or refute any sort of claim.

Right, what I meant to say was "there are no stats to support the claim that using liberal computers is more likely to result in DCS than using conservative ones." I really thought I was clear on my intent; and notice I said "don't support" which I suppose is a poor way of putting it. I understand that there are no stats which actively refute or support the claim of "liberal=risky/conservative=safe". I think we're in agreement on this, I just should have used clear language.

However, in this case, the absence of any stats which indicate variance in safety among various algorithms, in the presence of many thousands of dives with all the algorithms, tends to make me think that it is unlikely that there is a practical difference in the probability of getting DCS with different computer algorithms, again in strictly single tank dives within NDL limits (or planned to be).

Floater makes a good point; does DAN define "within limits" solely as NDL limits, or are ascent rate "violations" included? I'd be really surprised if they were, because I know how easy it is to set off the ascent alarm.

Snowbear, sorry I misunderstood...since the quote you took from my previous post was about the alleged safety differences between algorithms, I assumed your response "some people have said this" was referring to the statement in the quote.

 

[asaara]

I can only quote the figures that i have access to. I would be surprised if the 1997 figure would be substantially different from the current figure - ie I think we could guess that current figures would be somewhere in the same ball park. Even if we supposed the current figure was now say 80% (I just made that figure up for the sake of the argument - I have no reason to believe it would have changed that much) it would still represent a very high rate of bends from dives that computers are saying are quite safe.

But back in 1997, user replaceable batteries weren't quite so common, and algorithms get modified, so there may well be a significant amount of change, also what percentage (and type) of divers used computers back then compared to now? And you also can't tell how old the computers they were using at the time were, either, so newer stats would be nice...maybe a poll of some sort even here would pull up some stats? Would "ambulance chasing" in the accidents forum to see if they were diving within limits, and if so, with what, be incredibly rude and insensitive?

*Apparently mandatory disclaimer: Wanting to know more about DCS rates within limits on various computers does *not* necessarily imply people intend to dive their computers right to the limits and forget about thinking...

 

[asaara]

Some people have said this. No matter how it's presented though, It's pretty much always dismissed as a "closed-minded technophobe rant" with a justification such as the one here tacked on: "...No, I'm *not* looking for a computer to replace my brain, but for backup - I don't intend to turn my brain off entirely, but I would still like a *safe* backup..."

Maybe I'm expecting too much, but as board staff, don't you have better things to do than randomly flame people who may not have quite the same level of mathematical competence at 100fsw simply because they want to know who's computers are letting the most people get, according to the computer in question, "undeserved hits"? Just because you shouldn't *need* to rely on something doesn't mean it doesn't matter how reliable it is. Or is there currently insufficient flamebait in the bp/w and accidents forums?

And I'm not entirely sure how *my* quote qualifies me as a closed minded technophobe, as I *am* looking for a computer, or someone that rants about those people, as I never have. I only rant about people saying I deserve to get DCS simply because I want a computer at all, and don't want it to be pretty much useless when it's needed, when they most likely dive with computers themselves. "Buy a backplate!" when someone is asking which jacket BCD is best is still far more useful than "You're an idiot!" when someone asks what kind of computer is reliable.

 

[TheRedHead]

We recently went on a dive trip to Bonaire and both of our Sherwood Wisdom computers died within 2 days of each other. I had brought a backup Aeris Atmos Pro with me and gave it to my buddy when his croaked first with a flooded battery compartment. Mine blew out an O-ring so we rented a Suunto. I can't remember the model, but it was the cheap white one that was hard to read and had tiny silver buttons. I didn't care for it, but it was more liberal than the Aeris with the default settings.

We had to test this of course, so we dove a deep reef to 132 feet and the Aeris ran out of minutes before the Suunto. I'm attaching a pic of the computer and you can see that it is easy to read, even at depth.

 

[TheRedHead]

And I'm not entirely sure how *my* quote qualifies me as a closed minded technophobe, as I *am* looking for a computer, or someone that rants about those people, as I never have. I only rant about people saying I deserve to get DCS simply because I want a computer at all, and don't want it to be pretty much useless when it's needed, when they most likely dive with computers themselves. "Buy a backplate!" when someone is asking which jacket BCD is best is still far more useful than "You're an idiot!" when someone asks what kind of computer is reliable.

Asaara,

Just ignore it. Of the 13 reasons not to use a computer, I found only one credible reason that would apply to non-deco dives and that was that computer users would neglect to note their residual nitrogen group. If you had to go to tables in case of a computer failure, then you wouldn't be able to caculate the correct NDL on the repetitive dive.

Most divers are using computers and obviously you think about what you are doing and you are not going to become a mindless drone who obeys your computer. I've read many articles that suggest most so-called undeserved hits are probably caused by too fast ascents and a computer will alert you if you are exceeding the 30 ft/min. rate. That is a very positive reason to use a computer.

 

[asaara]

Most divers are using computers and obviously you think about what you are doing and you are not going to become a mindless drone who obeys your computer. I've read many articles that suggest most so-called undeserved hits are probably caused by too fast ascents and a computer will alert you if you are exceeding the 30 ft/min. rate. That is a very positive reason to use a computer.

Thanks for the info! Having not even been able to poke behind the glass in the display case (hey, why do salespeople stalk me like they're convinced I'm going to steal some shower gel in the Body Shop, but never come anywhere near me if I'm in an electronics store, anyways?), let alone been allowed to play around with someone else's computer, how do they display your residual nitrogen, exactly? Is it just on the bar graph and factored into the time remaining the next time it gets in the water, do they give you a table compatible type number or letter at the end of the dive and it counts down on the surface, or some other way?

Unless it's an emergency, my ears are quite likely to alert me in a more obvious fashion than the computer would if I'm exceeding the recommended ascent rate, so I don't tend to be racing with my bubbles. (my ears don't cause *me* problems, only other people, I just prefer to ascend/descend very slightly slower than some, meaning I don't have many fans among those that have a desperate need to be the first one down when they're the last off the boat...relax, isn't this supposed to be enjoyable?)

 

[halocline]

Unless it's an emergency, my ears are quite likely to alert me in a more obvious fashion than the computer would if I'm exceeding the recommended ascent rate, so I don't tend to be racing with my bubbles.

I doubt that your ears alert you to ascent rate issues in the way a computer will; the computer's ascent rate display is usually a series of indicators that appear to track your rate. Typically they're very sensitive, to the point where it's really difficult to not light up all the indicators, showing too fast ascent, at some point in a dive. (Lifting your arm can easily do this) This is why you usually have to exceed the ascent rate for a few seconds to set off the alarm.

As far as your display questions, I think there's a demo on the aeris website. You should be able to "play" with an online computer without any salesmen giving you a hard time. There are different displays when you're in the water (dive mode) and on the surface (surface mode) Dive mode will always display depth and NDL, and surface mode usually has surface time and a "plan" display, which basically scrolls through various depths, displaying NDL for each given depth if you were to re-enter the water at that moment.

 

[TheRedHead]

Unless it's an emergency, my ears are quite likely to alert me in a more obvious fashion than the computer would if I'm exceeding the recommended ascent rate, so I don't tend to be racing with my bubbles. (my ears don't cause *me* problems, only other people, I just prefer to ascend/descend very slightly slower than some, meaning I don't have many fans among those that have a desperate need to be the first one down when they're the last off the boat...relax, isn't this supposed to be enjoyable?)

Computers are more sensitive than your ears and it's annoyingly easy to set off the alarm. None of the computers I have used display residual nitrogen in anything other than a bar graph. I look up my group after each dive then log it. You can't do away with your tables and you should dive with tables in your pocket just in case.

Unless you are doing very deep dives and/or long dives with bigger tanks, it is unlikely that one buddy will hit the NDL before the other regardless of their computers. If you are diving AL 80s using conservative profiles, it probably won't matter if your buddy uses a more liberal/conservative computer. The depth and time of the safety stops may be somewhat different among different brands.

 

[WarmWaterDiver]

Personally, I thought the statistics presented by Undercurrent in their May 2005 issue were quite interesting - of the groups presented, the group with the highest incidence of DCS statistically were Scapa Flow divers who were diving square profiles - not something a multi-level dive computer has influence on. The data were on dives between 1998 and 2002, so of course some will want to see newer data - I would too, so if someone has some, please present it - share it with the class.

Cozumel dive guides, who when we were there in 2001 definitely did NOT do square profile dives (and the ones we dove with did use dive computers - often ones they had found on the reefs dropped by tourists - no surprise with the dive population density there), and who had the highest dive frequency of the groups presented, had the second highest rate of DCS statistically, had about 9 times the number of dives per diver than the Scapa Flow square profile divers and yet had significantly lower incidences of DCS than the square profile cold water divers.

Shore and day boat divers had the next lowest statistical frequency of DCS cases, and liveaboard divers had the lowest frequency of DCS cases by far of these 4 groups presented. By frequency, I'm saying my perspective is the most important statistic to me was the number of DCS cases per 10,000 dives in the data presented. The number of DCS cases per diver was less meaningful data to me, due to the wide difference in number of divers in each group in the data, other than to tell me it's best for me to stick to my 'day job' and keep scuba as a hobby rather than a profession - but I already knew that was correct for me just based on my personal preferences. That data showed the Cozumel dive guides were the most likely to get bent - and was the smallest 'number of divers' group by far in the four groups studied. So, statistically, the more you dive, the more chance you have to get bent - just like the more miles or hours you drive, the greater the statistical chance for you to be in a vehicle accident.

I personally think the proper use of a dive computer is sensible, so much so that I routinely use 2 such tools these days, but I do understand the apparatus I'm using. I first used math regarding half-times in school in relation to understanding radioactive substance decay, and chemical reaction kinetics, long before I took up scuba as a hobby. Today, I would use a PC and a spreadsheet or even highly complex and specialized software that I understand how to use for those applications, instead of a pocket calculator with pencil & paper alongside, just as today I choose to use a dive computer.

I'm a bit at a loss for those who say they wouldn't know their repetitive N2 group if they used a dive computer instead of square profile tables or devices like the PADI wheel. The dive computer models I choose to use display "time to desaturation" as calculated by the algorithm used - and this can be a figure well in excess of the 6 hours shown on the PADI square profile tables to return to "Pressure Group 'A'". I can personally use the theoretical 'time to desat' as something analagous to 'what repetitive N2 group am I in' - but I certainly can leave each to their own chosen methods as well. I also understand 'undeserved hits' occur and there is no such animal as 'perfectly safe - guaranteed no possibility of bends' just as adequately as I understand each time I drive my truck I am not 'perfectly safe' but operating within my knowledge base.

Each individual has their own personal set of choices to make and the variety of information presented here is of significant value. It's a shame the constructive tone takes a back seat once someone has a difference of opinion in so many cases - myself included at times.

So, anyone else have opinions / perspectives on what they took away from the Undercurrent May 2005 issue story on this topic? I'd like to see other perspectives I can learn from. Thanks.