Ambitious newb: Researching PDCs and relevant background info

[lv2dive]

I kind of take offense at your response. I actually explained WHY there was no value. I can't manufacture a value for something that does not exist because you want me to!

One of my first responses was a suggestion to purchase a simple Nitrox computer such as a Veo (which I believe, btw, can be run in gauge mode). Behind that suggestion was the understanding that based on your responses here and in other threads, you will unlikely be satisfied with diving recreationally for long. The Veo is an inexpensive computer which will meet all your recreational NEEDS while you actually get a few dives under your belt so that you can put all of these response in context.

If you are asking about recreational diving, an AI DC is an extra gimmick with limited value. (one feature some people like is "time remaining at current consumption/depth" - but I would rather figure that out in my head than rely on a computer, because the DC is not taking into account my buddy!) Just about all information available via other mechanisms, requires analog backup, prone to failure, encourages people to rely on computer vs. thinking. But hey, a lot of people like them, me, I'd rather spend the extra money elsewhere.

If you are asking/talking about technical diving, (and you continue to do so) the AI DC provides *no value* for the tech diver. YEP - I said it again. I am not going to say the "extra check and balance would be nice but..." if it is NOT going to add value. The AI Transmitter would be an extra failure point with ZERO benefit. If you don't change your gasses on your computer correctly, the deco/loading the computer calcs ON THAT DIVE and every successive dive will be off (as I mentioned in an earlier post). But the AI DC isn't going to have some magic way of telling you that. And as a tech diver you would have figured it out anyway.

It is absolutely commendable to want to get as much of an understanding as possible before moving into an endeavor but there are some things that have to be experienced.

I think I understand perfectly well the answers I've been given. I have almost no diving experience, but I have a LOT of experience with activities that can get you killed and using processes with checks and balances to ensure that you don't make a mistake and die. I understand very well the concepts of planning and redundant processes to cover contingencies that shouldn't happen but do anyway.

What I also think is that the people responding to me don't understand me. They all respond (including yours) as if I'm suggesting something that would replace any of their existing checks or balances or knowledge or experience - which I am not. Several responses have even addressed the issue of physically switching to the wrong gas, which I have never brought up as a scenario.

All I have asked about is the possibility that you make a mistake during the process you are already using, with your existing equipment - i.e. that you select the wrong gas on your PDC. And all the responses so far indicate that, either, nobody EVER makes that mistake, or, that everyone always follows their processes and checks and balances so perfectly that if they ever did make that mistake, they would catch it immediately (or close enough that it makes no difference). Either way, all responses indicate that there is NO value in an additional check-and-balance being added to the process. None of the responses have said "well, yes, that extra check-and-balance would be nice, but it's not worth the extra money." None of them have said, "well, yes, that extra check-and-balance would be nice, but it's not worth the tradeoff in questionable reliability of a wireless SPG - even if it's backed up by a traditional one."

Nope, all the responses to this question have either been "there is no value in that extra check-and-balance" or they've been off-topic (talking about physically switching to the wrong gas).

---------- Post added September 8th, 2014 at 03:35 PM ----------

BTW - My suggestion for a VEO has nothing to do with any great love for Oceanic or the VEO - it's just the only Nitrox wrist computer I am aware of, off the top of my head, for less than $200 that I think also runs in gauge mode.

 

[stuartv]

I kind of take offense at your response. I actually explained WHY there was no value. I can't manufacture a value for something that does not exist because you want me to!

My sincerest apologies if I have given offense. I certainly didn't mean to. I thought I was just stating what you and other said. Which you seem to be saying again. I said that you and others have said there is no value to AI (and yes, it was in a Tech diving context).

I elaborated to make it clear that the message I got was NOT that the value is not worth the tradeoffs - the message is that the value is 0. It wouldn't matter if the Petrel came with free AI at no extra cost - the Tech divers that have responded here would not use it.

I did not include a reiteration of the reasons given for the lack of value - other than the summary that, either, the diver does not make any mistakes, or there mistakes are caught by the process they are already using.

If I gave offense, I can only conclude that I have somehow misunderstood what you all have been telling me, in some way. Which is ENTIRELY possible. Please explain how I gave offense. I'd really like to understand what I'm not getting here.

If you don't change your gasses on your computer correctly, the deco/loading the computer calcs ON THAT DIVE and every successive dive will be off (as I mentioned in an earlier post). But the AI DC isn't going to have some magic way of telling you that.

As an example, I am clearly not understanding you correctly on this. You said if the diver doesn't change gases on the PDC correctly, the AI DC doesn't have some way of telling you that.

And I said, if you change gases (physically) correctly, but change the gases on your PDC incorrectly, the AI DC WILL tell you that. And it's not magic. It's the fact that the PDC will detect that the pressure is not dropping in the bottle that you told it you are using.

What am I not getting here?

 

[Dr. Lecter]

You said if the diver doesn't change gases on the PDC correctly, the [non-]AI DC doesn't have some way of telling you that.

This is incorrect, in at least one relevant case. Read the manual for the Petrel and you'll see why.

 

[stuartv]

This is incorrect, in at least one relevant case. Read the manual for the Petrel and you'll see why.

I am very unclear on what you're saying is incorrect. My best guess is that you are saying katepnatl is wrong and that the Petrel (which is non-AI) does have a way to tell the diver if they selected the wrong gas on their PDC.

Is that what you meant?

 

[Dr. Lecter]

I am very unclear on what you're saying is incorrect. My best guess is that you are saying katepnatl is wrong and that the Petrel (which is non-AI) does have a way to tell the diver if they selected the wrong gas on their PDC.

Is that what you meant?

Read the manual and figure it out, or don't. I've spent quite enough time on your questions.

 

[stuartv]

Read the manual and figure it out, or don't. I've spent quite enough time on your questions.

Well, you quoted (me, who was quoting) katepnatl. She said that AI computers don't have some magic way to detect that a diver chose a gas on their PDC that is not the same as the gas they just physically changed to. I pointed out that the AI PDCs DO have a way to do that.

As I understand you, your point is that katepnatl was wrong and the Petrel is non-AI and it DOES have a way to alert the diver if they selected the wrong gas on their PDC.

I have now read the Petrel manual, as you suggested, and I see that the Petrel will display your selected gas in yellow to indicate there is a better gas choice available for decompression than the gas the diver has selected. Presumably, the reason for your post was to bring out this point as a rejection of the notion that a non-AI PDC will do nothing to alert the diver if they physically switch gases and then select the wrong gas on their PDC.

I think that's a very handy thing to know about the Petrel. Thanks for pointing it out!

 

[lv2dive]

I see that you read the Petrel manual and have answered the question for yourself. What *I* said was there was no "magic" way that an AI DC was going to tell you that you chose the wrong gas... based on your presumption of the fact that the computer is going to notice via the AI, that you not breathing that gas down. That is the part that I was responding to.

Yes, the Petrel - which I use - tells me if I have a "better" or "more appropriate" gas programmed as "active" for the depth I am at. Depending on my dive profile, there are times that the gas the Petrel thinks is most appropriate is NOT the gas that is, in fact, most appropriate for the dive I have planned, for all kinds of reasons. So I note the yellow highlight and go on. I didn't really feel the need to go down this path about the details of how one non-AI DC functions. There is another non-AI DC (used primarily by "tech divers") that AUTOMATICALLY changes your gas depending on your depth. I think that is a TERRIBLE idea but some people really like it - I guarantee you they do not do a lot of cave diving though!

I am very unclear on what you're saying is incorrect. My best guess is that you are saying katepnatl is wrong and that the Petrel (which is non-AI) does have a way to tell the diver if they selected the wrong gas on their PDC.

Is that what you meant?

---------- Post added September 8th, 2014 at 06:30 PM ----------

I am just not clear what the computer is going to do/say... does it flash when you aren't breathing from the right bottle? What is it going to do when the reg of one your deco bottles purges and all of sudden the pressure reading is zero? Does it think you breathed your O2 at depth and tell you that you are going to tox? Does it calculate that your SAC rate just shot through the roof? (By the way - I really don't want an answer - I am just saying there are so very many different things that could happen during a tech dive that I can't imagine a AI DC accounting for them in a way that makes any kind of sense.)

You said earlier you like to KISS... Tech divers in general are about bringing exactly what they need, and no more... the ultimate in KISS. AI is a needless complication with no benefit. Yes, tech divers make mistakes. And we have processes and procedures in place to try and prevent those mistakes from going too far. But hundreds of divers and instructors with thousands of hours of experience have come to the conclusion that AI isn't going to do anything more than needlessly complicate things. It would not be an additional "check and balance". However, it is all but impossible to explain that to someone with no experience with technical diving, and it is quite clear that it IS impossible to explain in this forum. Perhaps some day in person?

And I said, if you change gases (physically) correctly, but change the gases on your PDC incorrectly, the AI DC WILL tell you that. And it's not magic. It's the fact that the PDC will detect that the pressure is not dropping in the bottle that you told it you are using.

What am I not getting here?

 

[stuartv]

I see that you read the Petrel manual and have answered the question for yourself. What *I* said was there was no "magic" way that an AI DC was going to tell you that you chose the wrong gas... based on your presumption of the fact that the computer is going to notice via the AI, that you not breathing that gas down. That is the part that I was responding to.

I am just not clear what the computer is going to do/say

I believe that all it's going to do is, if you tell it you switched to Gas 2, and the TX for Gas 2 indicates that pressure is not going down, it will display an alert - maybe even sound an audible alarm. That's it. Now you are the one making it too complicated. And it doesn't even have the built-in presumption (which you've already indicated is not always correct) to tell you which gas to use. It simply tells you "hey, you said you're using Gas 2, but Gas 2 isn't going down. Just FYI."

Tech divers in general are about bringing exactly what they need, and no more.

I've read enough here to know that if that were true, you would not take a PDC at all. And I'm not saying that because *I* know it. I'm saying it because I've read plenty of posts from experienced technical divers who say that all they need (and NEED is the word you used) is a depth gauge and a bottom timer - with a backup of each for redundancy.

You're taking a PDC for convenience. You use it to give yourself shorter deco stops (again, from what you have told me, not from my own experience) - shorter than are on your dive plan. It's a shortcut. A convenience. It doesn't even make you safer. It would be safer to stick to the deco stops on your dive plan, wouldn't it?

From other reading here, I gather that it also lets you track your nitrogen and oxygen debts more accurately, giving you increased bottom time on repetitive dives. But, isn't "more accurately" just another way of saying "with less safety margin" in this context?

Now, don't take all that the wrong way, I'm not suggesting you should stop using a PDC and go back to strictly diving tables or anything. I love technology and the improved accuracy it brings to activities like diving exactly because it allows you to have longer bottom times and/or shorter deco stops. I think it's awesome! I'm just pointing out that your argument of "we don't use AI because it's not necessary and we eliminate things that aren't necessary" seems to be at odds with the fact that you use a PDC at all.

 

[lv2dive]

I believe that all it's going to do is, if you tell it you switched to Gas 2, and the TX for Gas 2 indicates that pressure is not going down, it will display an alert - maybe even sound an audible alarm. That's it. Now you are the one making it too complicated. And it doesn't even have the built-in presumption (which you've already indicated is not always correct) to tell you which gas to use. It simply tells you "hey, you said you're using Gas 2, but Gas 2 isn't going down. Just FYI."

And what is it going to do when one of my deco regs purges? Is it going to tell me that i am breathing something I shouldn't be?

I've read enough here to know that if that were true, you would not take a PDC at all. And I'm not saying that because *I* know it. I'm saying it because I've read plenty of posts from experienced technical divers who say that all they need (and NEED is the word you used) is a depth gauge and a bottom timer - with a backup of each for redundancy.

You're taking a PDC for convenience. You use it to give yourself shorter deco stops (again, from what you have told me, not from my own experience) - shorter than are on your dive plan. It's a shortcut. A convenience. It doesn't even make you safer. It would be safer to stick to the deco stops on your dive plan, wouldn't it?

From other reading here, I gather that it also lets you track your nitrogen and oxygen debts more accurately, giving you increased bottom time on repetitive dives. But, isn't "more accurately" just another way of saying "with less safety margin" in this context?

Now, don't take all that the wrong way, I'm not suggesting you should stop using a PDC and go back to strictly diving tables or anything. I love technology and the improved accuracy it brings to activities like diving exactly because it allows you to have longer bottom times and/or shorter deco stops. I think it's awesome! I'm just pointing out that your argument of "we don't use AI because it's not necessary and we eliminate things that aren't necessary" seems to be at odds with the fact that you use a PDC at all.

I started to respond and realized there is nothing to be gained. I've tried to explain different perspectives to you but it is pretty clear that all you want to do is prove your point; I don't see any desire on your part to understand the thought process/philosophy behind anything anyone else has said. I truly hope that you go into tech diving some day so you can look back on this thread through different eyes.

 

[Tony387]

Nothing to say, but "wow."

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