You CANNOT Backup a Broken Computer by Tables (LONG)
Reef Fish
exchange with Matthias Voss, in which he was running around in circles
so much that he forgot where HE started from one post to the next!
So, I'll pick it up from there, and make this a GENERAL post,
"You CANNOT Backup a Broken Computer by Tables",
and reference a few articles of mine back in the early 1990s to show
that the substance of the topic "Computers vs Tables" hasn't changed
one bit, in spite of more bells and whistles on the newer computers
and more unsupported claims. The fact remains:
Matthias Voss <mat.nos...@t-online.de> wrote in message
news:<3D98C7FF...@t-online.de>...
> Reef Fish schrieb:
> > You CANNOT backup a broken computer by tables.
First, let's watch Matthias mouth-dance:
MV> Yes you can. All it needs is memorizing time into the dive and max
MV> depth. From thence on, the table comprises an envelope which integrates
MV> everything needed to complete the dive to a successfull ending.
Note the KEYWORDS "All it needs", which was why I gave Matthias an
example of what he asked for, as all it needs for him to back up a
failed dive computer with his tables:
RF> Day X. Dive 1. 199 fsw, 60 min. 90 min SIT.
RF> Dive 2. 150 fsw, 50 min. 3 hr. SIT.
RF> Dive 3. 180 fsw, 75 min. 90 min SIT.
RF> Dive 4. 120 fsw, 90 min.
RF>
RF> These are all NO DECO dives, according to my dive computer.
RF> Let's say the computer broke after Dive 3. Now let's see YOU back
RF> it up with your tables.
Now Matthias starting waffling and making excuses ... FIRST:
MV> Sorry , you are not giving the bottom times here, which I would
MV> need to visualize the deco obligations.
So I explained that the minutes given ARE the dive computer bottom times,
and gave him the actual definition used by the computer:
RF > Now use this definition of "bottom time" (the time spent underwater
RF > below 7 fsw), and work out problem I posed which you side-stepped
RF > with all kinds of excuses, on your tables, and see how MISERABLY
RF > you would fail.
Matthias, having mouth-danced through his hat for so long in the thread,
had already forgotten where HE started two posts back ("All it needs
is memorizing time into the dive and max depth."), now changed his tune:
MV> All this is irrelevant until you come up with a logges profile,
MV> which may be further evaluated.
What??? What happened to that "All it needs" claim of yours? Now you
want to know the detailed profile logged by the COMPUTER?
Matthias Voss running around in circles, delivering NOTHING he said he
could do with his tables, at the start.
----------------------------------------------------------------------
Next, Matthias changed his tune once more, and now complained that the
example I gave was "well beyond the models of any computers":
Note the KEYWORDS: "well beyond the models of any computers".
MV > The short surface intervals, as well as a number of 4 dives on one day
MV > put you well beyond the models of any computers, in spite of their
MV > claims.
To which I responded,
RF> That statement only shows your ignorance about dive computers as
RF> well as inexperience with REAL computer diving!
and asked Matthias his statement was "according to WHOM?"
MV > It is citing Ernie Voellm of Uwatec/Divetronic,
That's just the beginning of name-dropping while he FAILED to
substantiate his case of "backup up a broken computer with tables".
>
RF> Failing to support any of your points, you're now resorting to
RF> name-dropping.
RF>
RF> It so happens that Ernie was the person who did the Uwatec simulation
RF> for me on the Cochran data!! I was going 4 dives a day then, on
RF> a liveaboard, with even shorter surface intervals. Ernie was able
RF> to show that NONE of my series of 6 dives came anywhere close to
RF> the NDL boundry, including the one Cochran;s Nemesis PRO diagnosed
RF> to have missed 52 minutes of a 55-minute obligated deco.
Of course by now Matthias had forgotten he cited Ernie for Matthias's
own BULLSHIT about 4 dives on one day ... etc being "well beyond the
models of any computers" and that my paragraph above was given as a
DIRECT CONTRADICTION (by Ernie Voellm) to Matthias's false claim,
falsely attributed to Ernie, whom he thought I wouldn't know.
Once more, Matthias mouth-danced around another circle HE started, and
could do no better than muttering something non sequitur,
MV> So the computer was at fault ?
Matthias, what's AT FAULT is the ATTENTION SPAN of your brain, your
lack of logic, your lack of substance, and your lack of ability to
follow even a tiny sub-thread started by yourself! You are just
running around in circle chasing your own tail, while missing all
the RELEVANT points.
-----------------------------------------------------------------------
Now let me turn to the general readership on this topic, to give a few
pointers to those on what SHOULD have been known by them YEARS ago, had
they been diving that long ...
Prior to that round, I had said to Lee and Matthias,
RF> This pretty sums up all I have to say in this thread, if for no other
RF> reason that I'll be on the road for the next few days. Just read ANY
RF> of my posts about DIVE COMPUTERS in the archives since 1992 or before,
RF> and you'll see the same lessons -- pity you never learned them, not
RF> even now.
The only reason I said 1992 or before is that BEFORE 1992, I've posted
under names that are NOT "Reef Fish", but my userids RFLING and RFLNG
and addresses that had BITNET in them. It was 1992 when scuba postings
were getting so NUMEROUS for me that I changed my posting name to "Reef
Fish (Large Nassau Grouper)" which served as the anti-acronym for my
existing userid RFLNG, and began using it exclusively for scuba posts.
By 1992, I had already been diving with computers for FIVE years, and
had already read many of the TIMELESS scientific references that are
applicable TODAY.
If anyone does a groups.google.com advanced search using ONLY "Reef Fish"
as the author, and "computers OR computer" as the keyword, you'll find
AT LEAST 657 hits of posts of mine dating back to 1992.
If you search using ONLY "Reef Fish" as the author and 'any of the words'
"computer computers table tables", you'll find at least 731 hits. :-)
http://groups.google.com/groups?selm=910418042...@relay1.UU.NET
Among these hundreds, here are a few that may be worth repeating, for
the several different ongoing threads on the "computers vs tables" topics.
"Re: To compute or not to compute"
04 Oct 1992 by Reef Fish (Large Nassau Grouper) - Thread (31 articles)
Go to groups.google.com advanced search with
Message-ID: <SCUBA-L%9210041...@BROWNVM.BROWN.EDU>
The article addressed the subject in question and the PRESENT subject.
"Re: Dive computer vs. Table"
16 Jan 1995 by Reef Fish (Large Nassau Grouper) - Thread (8 articles)
Go to groups.google.com advanced search with
Message-ID: <SCUBA-L%9501161...@BROWNVM.BROWN.EDU>
This article REVIEWS NUMEROUS posts of mine on the subject, BEFORE
1995. It also addresses the question of DIVE SAFETY using computers.
"Dive Computers and Safety"
14 Feb 1996 by Reef Fish (Large Nassau Grouper)
Go to groups.google.com advanced search with
Message-ID: <SCUBA-L%9602141...@BROWNVM.BROWN.EDU>
This article reviews the topic as well as making reference to several
articles of mine posted in 1990 which is every bit true TODAY!!
Folks, this is how OLD the subjects are (with answers KNOWN a decade
ago) that many of you are still fumbling with today.
Barring exceptional follow-up points made by anyone, my general reply
to all would be:
1. Review the threads and related topic(s) in the archives over the
past decade.
2. Read a few books and scientific literature about dive computers.
3. Read a few books about DCI and decompression PHYSIOLOGY to learn
once and for all that NO TABLE and NO DIVE COMPUTER can make
YOUR dive safe for you, without knowing the important factors
about YOU that are not in the INPUT for tables or computers.
The bottom line HAS BEEN, and WILL BE (especially for multilevel dives):
"You CANNOT Backup a Broken Computer by Tables"
-- Bob.
Stephen Kenney
Large_Nass...@Yahoo.com wrote on 10/5/02 8:42 PM:
>
> Note the KEYWORDS "All it needs", which was why I gave Matthias an
> example of what he asked for, as all it needs for him to back up a
> failed dive computer with his tables:
>
> RF> Day X. Dive 1. 199 fsw, 60 min. 90 min SIT.
> RF> Dive 2. 150 fsw, 50 min. 3 hr. SIT.
> RF> Dive 3. 180 fsw, 75 min. 90 min SIT.
> RF> Dive 4. 120 fsw, 90 min.
> RF>
> RF> These are all NO DECO dives, according to my dive computer.
According to the computer these were no deco dives. Who's in charge, you or
the computer Bob, were these no deco dives?
> RF> Let's say the computer broke after Dive 3. Now let's see YOU back
> RF> it up with your tables.
I haven't seen any tables for dives this deep but then again I didn't look
because I don't dive that deep. Good thing you've got that computer. Who's
getting his lunch?
Greg Mossman
news:B9C50E47.2B50D%sfke...@earthlink.net...
> > RF> Day X. Dive 1. 199 fsw, 60 min. 90 min SIT.
> > RF> Dive 2. 150 fsw, 50 min. 3 hr. SIT.
> > RF> Dive 3. 180 fsw, 75 min. 90 min SIT.
> > RF> Dive 4. 120 fsw, 90 min.
> > RF>
> > RF> These are all NO DECO dives, according to my dive computer.
>
> According to the computer these were no deco dives. Who's in charge, you
or
> the computer Bob, were these no deco dives?
Obviously Bob was in charge since it was his computer. He followed the
computer, and obviously lived. It's assumed by his lack of mentioning any
obligatory deco stops that these were no deco dives. So what are you really
asking?
> I haven't seen any tables for dives this deep but then again I didn't look
> because I don't dive that deep. Good thing you've got that computer. Who's
> getting his lunch?
So now you've qualifed your "method" to apply only for folks that don't dive
that deep, whatever "that deep" may be. Great. If I said I didn't dive any
deeper than 30' I'd bet I could prescribe a foolproof method of
computer-less safe diving: "dive as long as you want without exceeding 30'
and you'll live." That's helpful.
As for getting Bob's lunch, perhaps we'll spread it on your casket before
they pile on the dirt. Mayo and mustard?
nos...@all.please.net
Publish your method. Only when published can it be
evaluated.
Lee Bell
> According to the computer these were no deco dives. Who's in charge, you
or
> the computer Bob, were these no deco dives?
> I haven't seen any tables for dives this deep but then again I didn't look
> because I don't dive that deep. Good thing you've got that computer. Who's
> getting his lunch?
As much as it pains me to be supportive of Bob at this particular moment, I
was there for some of the dives he describes and have been part of many
discussions relating to them. These were no deco dives, by his computer,
buy his own statements and by his survival without having done deco stops.
Nobody has been more consistent in the position that all information used
during a dive, whether from a computer, table or anywhere else, must be
filtered through the organic computer we got as part of the life package.
The fact that you can't plan them on the tables you use is not a
condemnation of his point but, rather, a demonstration of the weakness of
yours.
Bob will eat his own lunch and, if you aren't careful, yours as well.
Lee
Stephen Kenney
lee...@ix.netcom.com wrote on 10/6/02 7:15 AM:
> Stephen Kenney wrote
>
>> According to the computer these were no deco dives. Who's in charge, you
> or
>> the computer Bob, were these no deco dives?
>
>> I haven't seen any tables for dives this deep but then again I didn't look
>> because I don't dive that deep. Good thing you've got that computer. Who's
>> getting his lunch?
>
> As much as it pains me to be supportive of Bob at this particular moment, I
> was there for some of the dives he describes and have been part of many
> discussions relating to them. These were no deco dives, by his computer,
> buy his own statements
That was then. I'm asking him now today if his opinion has changed because
many poeple think all dives are decompression dives.
>and by his survival without having done deco stops.
This isn't the best way to dive and decompress. Just because the high
precision computer didn't give Bob deep stops doesn't mean deep stops
wouldn't have been good for his health.
> Nobody has been more consistent in the position that all information used
> during a dive, whether from a computer, table or anywhere else, must be
> filtered through the organic computer we got as part of the life package.
If Bob chooses to plan dives to 200' he should get advanced training or
hookup with divers that know what they're doing. He seems perplexed that
there are no tables for his needs. There are, but they don't give them away.
> The fact that you can't plan them on the tables you use is not a
> condemnation of his point but, rather, a demonstration of the weakness of
> yours.
I don't feel any weakness at all setting my depth limit to relate to the
training and experience I have. It's your weakness not realizing that.
>
> Bob will eat his own lunch and, if you aren't careful, yours as well.
Anyone of us can be giving away lunches if we fuck up down there.
>
> Lee
>
>
>
Jason O'Rourke
>Before I went out of town a few days ago, I was in the midst of an
>exchange with Matthias Voss, in which he was running around in circles
>so much that he forgot where HE started from one post to the next!
poor Bob. No one to play with.
>RF> Day X. Dive 1. 199 fsw, 60 min. 90 min SIT.
>RF> Dive 2. 150 fsw, 50 min. 3 hr. SIT.
>RF> Dive 3. 180 fsw, 75 min. 90 min SIT.
>RF> Dive 4. 120 fsw, 90 min.
Nice real world examples!
Sit out the rest of the day. Start the next day with the table of your choice.
And yes, if I were doing bounce dives of these sorts, I'd want to spend some
time looking at programs like GAP.
--
Jason O'Rourke www.jor.com
Ross Bagley
> Before I went out of town a few days ago, I was in the midst of an
> exchange with Matthias Voss, in which he was running around in circles
> so much that he forgot where HE started from one post to the next!
>
> So, I'll pick it up from there, and make this a GENERAL post,
>
> "You CANNOT Backup a Broken Computer by Tables",
If you've been diving within recreational limits and were diving
within the NDL's according to the computer before the failure, it's
fairly safe to assume the nitrogen in your tissues can be modelled as
being within the NDL's on recreational tables and those tables can
then quite easily back up a broken computer.
It's really quite simple. Here's how:
If you can reconstruct your dives for the day on the tables (from your
dive log and/or your memory), do it and go diving. Otherwise, put
yourself in the most conservative pressure group on the tables and go
diving (this will cut into your bottom time as compared to a backup
computer).
Maybe "fairly safe to assume" isn't good enough for you or the diving
you do. Maybe bottom time is important enough that you've spent the
money on a backup computer. Mokay! (in either case) The assumed risk
level is certainly low enough for me and the diving I do. It's also
low enough for most other people once they grasp the logic of how to
back up a computer with tables.
Regards,
Ross
-- Ross Bagley http://rossbagley.com/rba
"Security is mostly a superstition. It does not exist in nature...
Life is either a daring adventure or nothing." -- Helen Keller
Lee Bell
> That was then. I'm asking him now today if his opinion has changed because
> many poeple think all dives are decompression dives.
I'm pretty sure I know the answer to this one, but I'll let him answer for
himself. I will, however, say that you're mixing definitions for
decompression dive. Every dive is a decompression dive, but not every dive
has mandatory stops. Mandatory stops is the common definition of
"decompression dive" even if it too is a misnomer.
> This isn't the best way to dive and decompress. Just because the high
> precision computer didn't give Bob deep stops doesn't mean deep stops
> wouldn't have been good for his health.
And nothing in Bob's post or mine means he didn't do them . . . or something
equally effective. In fact, there are some pretty clear hints that he did
something you have not taken into account. Somebody that descends to 200
feet and does a 60 minute dive, has done something he has not described in
detail.
> If Bob chooses to plan dives to 200' he should get advanced training or
> hookup with divers that know what they're doing. He seems perplexed that
> there are no tables for his needs. There are, but they don't give them
away.
You haven't a clue as to what Bob's training is. Sorry to be the one to
tell you, but you're not qualified to judge him, not by a long shot.
> > Bob will eat his own lunch and, if you aren't careful, yours as well.
> Anyone of us can be giving away lunches if we fuck up down there.
Yep. I've been diving for right at 40 years. I'm not sure how long Bob's
been diving, but I do recall he holds a 2000 dive card from SSI. I think
our lunches are reasonably secure. We're not sure about yours.
Lee
nos...@all.please.net
> Large_Nass...@Yahoo.com (Reef Fish) writes:
>
> > Before I went out of town a few days ago, I was in the midst of an
> > exchange with Matthias Voss, in which he was running around in
circles
> > so much that he forgot where HE started from one post to the next!
> >
> > So, I'll pick it up from there, and make this a GENERAL post,
> >
> > "You CANNOT Backup a Broken Computer by Tables",
>
> If you've been diving within recreational limits and were diving
> within the NDL's according to the computer before the failure, it's
> fairly safe to assume the nitrogen in your tissues can be modelled as
> being within the NDL's on recreational tables and those tables can
> then quite easily back up a broken computer.
>
> It's really quite simple. Here's how:
>
> If you can reconstruct your dives for the day on the tables (from your
> dive log and/or your memory), do it and go diving. Otherwise, put
> yourself in the most conservative pressure group on the tables and go
> diving (this will cut into your bottom time as compared to a backup
> computer).
Prove that you can't surface with a deco obligation from
every instant of a no-deco report from the computer.
>
> Maybe "fairly safe to assume" isn't good enough for you or the diving
> you do. Maybe bottom time is important enough that you've spent the
> money on a backup computer. Mokay! (in either case) The assumed risk
> level is certainly low enough for me and the diving I do. It's also
> low enough for most other people once they grasp the logic of how to
> back up a computer with tables.
Yes, sit out (at least)12 hours and dive by tables.
Is Ross Bagley willing to assume financial liability when
his method fails?
Ross Bagley
> "Ross Bagley" ro...@rossbagley.com writes:
[...snip...]
> Prove that you can't surface with a deco obligation from every
> instant of a no-deco report from the computer.
That's what my dive computer is marketed to accomplish and what I
bought it for. When the computer indicates that I can do a direct
ascent (when the computer indicates no decompression obligation), I
feel quite safe in doing a direct ascent to the surface. This
decision, is of course, moderated by the ol' grey matter, though my
dive computer has been extremely reliable for me (and thousands of
other divers using the same computer).
Do your dive computers do things differently? All three of them?
Perhaps you ought to make your next dive computer buying decision
based on quality rather than quantity and try to sell the three you've
got to some sucker on eBay.
As for proving that dive computers do what dive computers are supposed
to do... You do realize that DCS isn't fully understood and all of
the models that computers use (and tables are based on) only claim to
use fairly conservative assumptions about a "normal" human body?
Only a fool asks for certainty in a discussion of approximations and
risks. I'm reminded of a pointy haired boss recently asking me for a
firm date on a firm set of features with perfect quality. You too
can learn how reality works, though I'm not holding my breath.
> > Maybe "fairly safe to assume" isn't good enough for you or the diving
> > you do. Maybe bottom time is important enough that you've spent the
> > money on a backup computer. Mokay! (in either case) The assumed risk
> > level is certainly low enough for me and the diving I do. It's also
> > low enough for most other people once they grasp the logic of how to
> > back up a computer with tables.
>
> Yes, sit out (at least)12 hours and dive by tables.
>
> Is Ross Bagley willing to assume financial liability when
> his method fails?
I'm willing to accept personal responsibilty for my own dive safety,
even in the unlikely event that I need to switch to tables to keep
diving after a computer failure.
If someone else decides to use this strategy to continue diving after
a computer failure, they are still responsible for their own safety.
If they are not convinced that the practice I recommend is safe, they
should call the dive (I've seen it happen and I accepted that decision
without question).
You apparently, are not convinced of the safety of the practice, and
therefore shouldn't take that risk (this bit was covered in the first
sentence of my posting that you helpfully included above). Bob may
be another. That's fine. Everyone has their own risk tolerance and
I'm the first to say that you always have the right to call a dive.
For the rest of us, it's as safe as the dive computer or the tables in
the first place (which is pretty safe but not completely safe).
Personally, since I am rarely limited by the NDL's (I usually use
EAN32 and prefer shallow dives) and I am almost always out of gas
before the computer gets close to the NDL's, there is almost no time a
computer *could* fail that would leave me with a decompression
obligation that I didn't know about.
This is a common way of diving in the recreational dive world...
Unknown
spouted forth:
>nos...@all.please.net writes:
>> "Ross Bagley" ro...@rossbagley.com writes:
>
>[...snip...]
>
>> Prove that you can't surface with a deco obligation from every
>> instant of a no-deco report from the computer.
Well I cannot "prove" anything. But I have baled out from a broken
computer showing "quite a lot" of deco, on mixed gasses, to tables.
And I guess that as I'm still here I must have got it right.
So you CAN backup a broken computer with tables.
But I'm a stroke so what would I know....
Pete S.
Reef Fish
> Stephen Kenney wrote
>
> > That was then. I'm asking him now today if his opinion has changed because
> > many poeple think all dives are decompression dives.
>
> I'm pretty sure I know the answer to this one, but I'll let him answer for
> himself.
Thanks Lee. You answered this and other questions nicely. I wasn't
going to answer ANY of Stephen Kenney's frivolous questions which only
showed the DEPTH of his ignorance, since I had already said in my
initial post of this thread:
RF> Barring exceptional follow-up points made by anyone, my general reply
RF> to all would be:
RF>
RF> 1. Review the threads and related topic(s) in the archives
RF> 2. Read a few books and scientific literature about dive computers.
RF> 3. Read a few books about DCI and decompression PHYSIOLOGY to learn
-- Bob.
Reef Fish
> Large_Nass...@Yahoo.com (Reef Fish) writes:
>
> > Before I went out of town a few days ago, I was in the midst of an
> > exchange with Matthias Voss, in which he was running around in circles
> > so much that he forgot where HE started from one post to the next!
> >
> > So, I'll pick it up from there, and make this a GENERAL post,
> >
> > "You CANNOT Backup a Broken Computer by Tables",
>
> If you've been diving within recreational limits and were diving
> within the NDL's according to the computer before the failure, it's
> fairly safe to assume the nitrogen in your tissues can be modelled as
> being within the NDL's on recreational tables and those tables can
> then quite easily back up a broken computer.
>
> It's really quite simple. Here's how:
>
> If you can reconstruct your dives for the day on the tables (from your
> dive log and/or your memory), do it and go diving. Otherwise, put
> yourself in the most conservative pressure group on the tables and go
> diving (this will cut into your bottom time as compared to a backup
> computer).
Okay, I'll play. This was my original problem given to Matthias Voss:
RF> Day X. Dive 1. 199 fsw, 60 min. 90 min SIT.
RF> Dive 2. 150 fsw, 50 min. 3 hr. SIT.
RF> Dive 3. 180 fsw, 75 min. 90 min SIT.
RF> Dive 4. 120 fsw, 90 min.
RF>
RF> These are all NO DECO dives, according to my dive computer.
RF> Let's say the computer broke after Dive 3. Now let's see YOU back
RF> it up with your tables.
For YOU, Ross, just change the 199, 150, and 180 in the first three dives
to 130, and you'll have "within recreational limits" in the conventional
sense. I am easy. :-)
Tell us HOW you back up with tables when the computer failed, after
Dive 3, and tell us what your tables will say to a 120 fsw (Nax) dive
for 90 minutes, after a 90 minute SIT after Dive 3. :-))
-- Bob.
Lee Bell
> If you've been diving within recreational limits and were diving
> within the NDL's according to the computer before the failure, it's
> fairly safe to assume the nitrogen in your tissues can be modelled as
> being within the NDL's on recreational tables and those tables can
> then quite easily back up a broken computer.
>
> It's really quite simple. Here's how:
>
> If you can reconstruct your dives for the day on the tables (from your
> dive log and/or your memory), do it and go diving. Otherwise, put
> yourself in the most conservative pressure group on the tables and go
> diving (this will cut into your bottom time as compared to a backup
> computer).
Careful, you're about to be called names. That's the method Bob's been
calling Bullshit for years. In fact, there is a risk to it, but it's not
yet quantified. The risk is that there is a profile that a diver might
reasonably have done, that will result in him having no deco obligation at
the beginning of the dive, but having one by the time he reaches the
surface. While I've found a number of profiles that result in a small deco
obligation during the ascent, I've found none that are reasonably likely to
be done, that still have one at the surface. Bob hasn't come up with any
profile that will leave a diver with a deco obligation, in several years and
he's the self professed expert on computers.
For those of us that believe a next dive can be done safely enough, the
question is generally more about bottom time for remaining dives. I
sometimes carry a backup computer to ensure that I don't lose the dive time
that led me to buy one in the first place. Dive trips are expensive and
computers aren't.
Lee
Lee Bell
> RF> Day X. Dive 1. 199 fsw, 60 min. 90 min SIT.
> RF> Dive 2. 150 fsw, 50 min. 3 hr. SIT.
> RF> Dive 3. 180 fsw, 75 min. 90 min SIT.
> RF> Dive 4. 120 fsw, 90 min.
> RF> These are all NO DECO dives, according to my dive computer.
> RF> Let's say the computer broke after Dive 3. Now let's see YOU back
> RF> it up with your tables.
>
> For YOU, Ross, just change the 199, 150, and 180 in the first three dives
> to 130, and you'll have "within recreational limits" in the conventional
> sense. I am easy. :-)
>
> Tell us HOW you back up with tables when the computer failed, after
> Dive 3, and tell us what your tables will say to a 120 fsw (Nax) dive
> for 90 minutes, after a 90 minute SIT after Dive 3. :-))
They'll say that you can't do it. Nobody said that going to tables after a
computer failure would allow the same depth and time after a surface
interval. Almost everybody that's discussed the issue at all has
acknowledged that you're going to lose dive time to account for the
uncertainty about what the actual repetitive dive group is. By using the
most extreme group, you guarantee a loss of depth/time but, in doing so,
also ensure, as far as is possible, that you're plan is more conservative
than reality.
Just out of curiosity, and not because it is relevant to your point, what
did your computer planning screen show for that 4th dive, just before you
did it? I'll bet it didn't show you could dive to 120 feet for 90 minutes.
Lee
Stephen Kenney
Pop the head out for one minute. Now if there is possibility that you're
thinking of backing up a computer with a table then you need to be be
willing to switch to table definitions for bottom time which ends when the
ascent begins on a square profile dive which on these deep dives was about 4
minutes. If you want to play, play fair or pop the head back in, your little
game has gotten pretty childish. How much time passed before you began
ascending from the first dive at 199'?
nos...@all.please.net
> nos...@all.please.net writes:
> > "Ross Bagley" ro...@rossbagley.com writes:
>
> [...snip...]
>
> > Prove that you can't surface with a deco obligation from every
> > instant of a no-deco report from the computer.
>
> That's what my dive computer is marketed to accomplish and what I
> bought it for. When the computer indicates that I can do a direct
> ascent (when the computer indicates no decompression obligation), I
> feel quite safe in doing a direct ascent to the surface.
Then you clearly do not know how they work.
Ross Bagley
> ro...@rossbagley.com (Ross Bagley) wrote:
[...snip...]
> > It's really quite simple. Here's how:
> >
> > If you can reconstruct your dives for the day on the tables (from your
> > dive log and/or your memory), do it and go diving. Otherwise, put
> > yourself in the most conservative pressure group on the tables and go
> > diving (this will cut into your bottom time as compared to a backup
> > computer).
>
> Okay, I'll play. This was my original problem given to Matthias Voss:
>
> RF> Day X. Dive 1. 199 fsw, 60 min. 90 min SIT.
> RF> Dive 2. 150 fsw, 50 min. 3 hr. SIT.
> RF> Dive 3. 180 fsw, 75 min. 90 min SIT.
> RF> Dive 4. 120 fsw, 90 min.
> RF>
> RF> These are all NO DECO dives, according to my dive computer.
> RF> Let's say the computer broke after Dive 3. Now let's see YOU back
> RF> it up with your tables.
>
> For YOU, Ross, just change the 199, 150, and 180 in the first three dives
> to 130, and you'll have "within recreational limits" in the conventional
> sense. I am easy. :-)
>
> Tell us HOW you back up with tables when the computer failed, after
> Dive 3
For the PADI RDP, you're in pressure group 'Z' after a slow ascent
from the third dive given above.
Since you aren't bent and your computer always claimed you didn't have
a deco obligation, the nitrogen content of your tissues can be
modelled on the table somewhere. Since the table can't directly model
the multi-level dives you describe, however, we'll have to be
conservative as to which pressure group we choose to use. The most
conservative pressure group on the table is pressure group 'Z', so I
would recommend using that and get back in the water.
See? Quite simple. There's really nothing to it.
> , and tell us what your tables will say to a 120 fsw (Nax) dive
> for 90 minutes, after a 90 minute SIT after Dive 3. :-))
The PADI RDP would only allow a 6 minute dive to 120fsw after a 90
minute surface interval (since your pressure group at the start of the
fourth dive is 'F'). That is reduced 10 minutes from a maximum of 16
minutes by the conservative ascent pressure group on the third dive.
I don't say that you could do the same dive on the table as you could
on a backup computer, only that it is at least as safe to use a table
to back up a failed computer as it is to use the table in the first
place. Reduced bottom time on multi-level dives is the cost of using
tables at all.
Your assertion was that a table can't be used to back up a broken
computer. Which isn't true. What can't be done is to get the same
bottom time from a recreational table as from a recreational computer,
which has always been the case.
Ross Bagley
Ah, the glory of argument by repeated assertion.
You have made this assertion in the past, and even made up your own
language in your own little world to "substantiate" it, without ever
managing to come up with a useful statement in support of your first
assertion.
First, depending on the rate of ascent, well... of course... Your
computer can assert that you have no decompression obligation at
depth, you then rocket to the surface on the BC express: you're bent.
Any decent model would be able to tell you exactly why.
But at a 30fpm ascent rate? Not according to my dive computer.
That's the way it calculates NDL's (based on the outgassing available
during a 30fpm ascent from depth). As I stated in my last post, I
would stay away from any dive computer that would pop suprises like
that on you.
So, are you prepared to come up with a dive that you can profile with
the RGBM model where the model puts the diver within the NDL's until
some point during a 30 foot per minute final ascent where the model
suddently requires a stop?
Just one profile. Until then... BTW, I'd recommend warning Suunto
before posting it to the newsgroup, since such a profile would be a
demonstration that their dive computers don't actually accomplish
the design goals stated for them.
ben bradlee
Ross Bagley
[...snip...]
> Careful, you're about to be called names. That's the method Bob's been
> calling Bullshit for years. In fact, there is a risk to it, but it's not
> yet quantified. The risk is that there is a profile that a diver might
> reasonably have done, that will result in him having no deco obligation at
> the beginning of the dive, but having one by the time he reaches the
> surface.
Not with a 30fpm ascent from a dive within the RGBM model NDL's.
> While I've found a number of profiles that result in a small deco
> obligation during the ascent, I've found none that are reasonably likely to
> be done, that still have one at the surface.
Oh, you guys are talking about transient (false) obligations? I've
heard of those when you push the edge of some dive profile modelling
algorithms. I don't get them on my computer (Suunto Cobra).
> Bob hasn't come up with any profile that will leave a diver with a
> deco obligation, in several years and he's the self professed expert
> on computers.
Well, nospam has been making similar assertions since he first mentioned
that he carries two backup computers on each dive and got called on it.
> For those of us that believe a next dive can be done safely enough, the
> question is generally more about bottom time for remaining dives.
Exactly. But I haven't bought my second Suunto yet, so my backup plan
is to accept the reduced bottom time and fall back to tables.
> I sometimes carry a backup computer to ensure that I don't lose the
> dive time that led me to buy one in the first place. Dive trips are
> expensive and computers aren't.
I have yet to spend $1000 on a dive trip, though I understand your
point. For the next 6 months or so, it's unlikely that I will spend
more than $20/dive for any diving that I might do, what with needing
all of my money to start up another business...
Ross Bagley
> Imagination is more important than knowledge.
Did you have a contribution to make to the discussion or are
you just going to entertain us with gems from your own personal
philosophy?
You read like Jack Handy.
ben bradlee
"Imagination is more important than knowledge."
Albert Einstein
Ross Bagley
And that's relevant to this discussion how? Attributing the quote
broadens the context substantially, but doesn't make it's presence
any less bizarre in reply to my posting.
You still read like Jack Handy.
nos...@all.please.net
If you're advocating the method, then it is incumbent on you to
show that it is safe. I've already told you why there is reason
to doubt its safety. It's all on the archives.
Ross Bagley
> In <l5cu1jy...@panix3.panix.com> Ross Bagley wrote:
[...snip...]
> > So, are you prepared to come up with a dive that you can profile with
> > the RGBM model where the model puts the diver within the NDL's until
> > some point during a 30 foot per minute final ascent where the model
> > suddently requires a stop?
> If you're advocating the method, then it is incumbent on you to
> show that it is safe. I've already told you why there is reason
> to doubt its safety. It's all on the archives.
So, no. You're not prepared to come up with a demonstration of a dive
computer producing inconsistent data.
Fine by me.
Reef Fish
Googles posting/updating is a bit slow today. This is close to 12
hours
since I replied to Ross's first post, but I haven't even seen my OWN
post yet, let alone seeing Ross's reply about how HE could backup my
modified example (by changing all depths above 130 fsw to 130 fsw) to
"within recreational limits". Given what I have seen what he said,
and
my follow-up here, it appears likely I have already said what needs to
be said to him or some other past/future responses.
Keep this in mind when you read my comments (which *I* consider VERY
important in this thread) to a couple of points made by Ross and
nospam.
> You do realize that DCS isn't fully understood and all of
> the models that computers use (and tables are based on) only claim to
> use fairly conservative assumptions about a "normal" human body?
Wasn't this and related points covered in these in my initial post? :
RF> "Re: Dive computer vs. Table"
RF> 16 Jan 1995 by Reef Fish (Large Nassau Grouper) - Thread (8
articles)
RF> It also addresses the question of DIVE SAFETY using computers.
RF> "Dive Computers and Safety"
RF> 14 Feb 1996 by Reef Fish (Large Nassau Grouper)
Ross > The assumed risk
Ross > level is certainly low enough for me and the diving I do. It's
also
Ross > low enough for most other people once they grasp the logic of
how to
Ross > back up a computer with tables.
1. You HAVEN'T grasped the logic NOR have you found a method to back
up a computer with tables. This part is absolutely clear based on
what you wrote!
2. Don't extrapolate your own perceived risk and erroneously
perceived
(invalidly perceived as valid) method of backup to situations for
which your perception is DEAD WRONG, for others, based on nothing
but knowing HOW DIVE COMPUTERS WORK!!
nonspam> Yes, sit out (at least)12 hours and dive by tables.
I am leaving out this irrelevant part below:
nonspam > Is Ross Bagley willing to assume financial liability when
nonspam > his method fails?
Sitting out 12 hours (or even 24 hours) MAY allow one to start fresh
is applicable ONLY to TABLES throughout, but NOT to dive computers!!!
If you understand computer algorithms, compartments, M-values etc..
you'll realize that in a series of repetitive dives (even within a
single day, and ALL dives are within NDL), a COMPUTER algorithm may
NOT clear completely even after 24 hours, when there is sufficient
loading in the slowest compartments on the last dive.
Both ORCA and Uwatec computers have these LONG half-life compartments.
A simple empirical observation in the ORCA computers is to see how
many HOURS the divecomp will CONTINUE running (even after it has
cleared
"safe to fly", which often run up to 19 hours for some of my dive
days)
until it shows "turn me off now" (which indicates that ALL
compartments
are cleared), which may take ANOTHER 12 or more hours!!
It's only at THAT point when one is "safe" to RE-START fresh, with
tables or another computer, if you UNDERSTAND and believe how that is
the CORRECT information provided by the dive computer!
That is one reason why on ALL liveaboard diving, my dive computer
NEVER
stops running from the time I turn it on the first dive, until after
the entire trip is finished five days later, even though there are
plenty
of occasions of surface intervals of greater than 12 hours between
days.
Ross> Personally, since I am rarely limited by the NDL's
>
Ross> This is a common way of diving in the recreational dive world...
That's precisely the PROBLEM in your INVALID argument of trying to
extrapolate your OWN experience, which is NOT APPLICABLE to the
general framework/discussion of how dive computers work, or why it is
IMPOSSIBLE
to back up a failed computer by tables! As I said in my initial post:
RF> 1. Review the threads and related topic(s) in the archives over
the
RF> past decade.
RF>
RF> 2. Read a few books and scientific literature about dive computers
-- Bob.
Stephen Kenney
ro...@rossbagley.com wrote on 10/7/02 10:49 AM:
> What can't be done is to get the same
> bottom time from a recreational table as from a recreational computer,
> which has always been the case.
True, you can get more bottom time on some deeper dives with tables.
100' 25 minutes tables
100' 17 minutes Suunto
40' not exactly the same about 130 minutes for both tables and computer
Charlie Allen
"Ross Bagley" <ro...@rossbagley.com> wrote in message
news:l5cy99a...@panix3.panix.com...
It's easy to miscalculate using tables, particularly when there are a bunch of
exceptions buried in the fine print on the back.
While in general I agree with your computer-to-tables transition procedure, a 6
minute dive to 120fsw after 90 minute SI would violate the PADI/DSAT RDP in this
case. The fine print says that if your ending pressure group is Y or Z after
any dive in a series of 3 or more in one day, then the minimum surface interval
between each dive is 3 hours.
I haven't reverse engineered the PADI tables enough to know for sure, but
it looks like the table only takes into account the faster compartments; and the
"special rules for multiple dives" text adds in the extra SI that is needed when
you load up the slow compartments via repetitive, very long, shallow dives.
The NAUI tables don't have these exceptions, but also would prohibit the 4th
dive of the above series.
If you and your buddy have been staying close to each other, then you have an
additional data point about what sort of profile is reasonable for you to dive,
and extending the hang time at 15' is a reasonable way to account for small
variances in the profiles between you and your buddy, as is the additional
measure of spending the next dive 10' above your buddy.
If you are DIR, then none of the above matters since, instead of relying upon
your computer, you have been continuously calculating your deco requirement all
along.
Charlie Allen
Mike
>
> nos...@all.please.net writes:
>
> > In <l5cwuou...@panix2.panix.com> Ross Bagley wrote:
> > > nos...@all.please.net writes:
> > > > "Ross Bagley" ro...@rossbagley.com writes:
> > >
> > > [...snip...]
> > >
> > bought it for. When the computer indicates that I can do a direct
> > ascent (when the computer indicates no decompression obligation), I
> > feel quite safe in doing a direct ascent to the surface.
>
> the RGBM model where the model puts the diver within the NDL's until
> some point during a 30 foot per minute final ascent where the model
> suddently requires a stop?
>
This assumes that you are placing complete and total trust in the model
used to calculate the deco status. There are models out there that I am
not comfortable using without adding quite a bit of coservitism. Any
serious dive, I plan using at least two differing models to do a sanity
check on the profile. I use my computer as a 'OH SHIT' bailout for any
serious dives I do. Now here's the next question: What model does you
computer actually use? My old genesis is a ZL16B Beuhlman model with
some tweaking. (How much???). I use a ZL16C model with GF deep stops
as my preffered model. (I feel really good after the dives). Now, here's
a real world example of a dive that I have done and what my computer
told
me:
First, the plan:
20 minutes @ 50ft
10 minutes @ 150ft
2 minutes @ 70ft (50/50)
7 minutes @ 50ft (50/50)
1 minute @ 40ft (50/50)
1 minute @ 30ft (50/50)
12 minutes @ 20ft (50/50)
(for this dive, carrying single deco gas was simpler and gave only an
additional 4-5 minutes @ 20ft)
The actual Dive:
7 minutes @ 47ft
10 minutes @ 145ft
2 minutes @ 70ft (50/50)
7 minutes @ 50ft (50/50)
1 minute @ 40ft (50/50)
1 minute @ 30ft (50/50)
15 minutes @ 20ft (50/50)
During this dive, my computer told me that when I hit 70ft, 17 minutes
into the dive, I could go straight to the surface. Do you really want to
test your computers model on your actual body by using it to plan your
dives?
nos...@all.please.net
Allen" wrote:
> If you are DIR, then none of the above matters since, instead of
relying upon
> your computer, you have been continuously calculating your deco
requirement all
> along.
Streaks don't count.
nos...@all.please.net
> nos...@all.please.net writes:
>
> > In <l5cu1jy...@panix3.panix.com> Ross Bagley wrote:
>
> [...snip...]
>
> > > So, are you prepared to come up with a dive that you can profile
with
> > > the RGBM model where the model puts the diver within the NDL's
until
> > > some point during a 30 foot per minute final ascent where the model
> > > suddently requires a stop?
>
> > If you're advocating the method, then it is incumbent on you to
> > show that it is safe. I've already told you why there is reason
> > to doubt its safety. It's all on the archives.
>
> So, no. You're not prepared to come up with a demonstration of a dive
> computer producing inconsistent data.
There is no need to. I've already shown a hole in your
method large enough to dive a truck through.
Deal with it.
Ross Bagley
> "Ross Bagley" <ro...@rossbagley.com> wrote in message
[...snip...]
> > The PADI RDP would only allow a 6 minute dive to 120fsw after a 90
> > minute surface interval (since your pressure group at the start of the
> > fourth dive is 'F'). That is reduced 10 minutes from a maximum of 16
> > minutes by the conservative ascent pressure group on the third dive.
> It's easy to miscalculate using tables, particularly when there are
> a bunch of exceptions buried in the fine print on the back.
> While in general I agree with your computer-to-tables transition
> procedure, a 6 minute dive to 120fsw after 90 minute SI would
> violate the PADI/DSAT RDP in this case. The fine print says that if
> your ending pressure group is Y or Z after any dive in a series of 3
> or more in one day, then the minimum surface interval between each
> dive is 3 hours.
I didn't remember that little detail about the PADI RDP. Even after
you pointed it out, if I was to use a table to back up my computer,
I'd probably just put the ascent pressure group at 'Z' and happily
ignore this particular detail for my next dive plan.
My choice of pressure group 'Z' isn't based on really spending a lot
of time at shallow depths (and the real risks of these kinds of
dives), but is just being conservative about where my more "typical"
dives would actually be best modelled on the chart.
Ross Bagley
> ro...@rossbagley.com (Ross Bagley) wrote in message news:<l5cwuou...@panix2.panix.com>...
> > You do realize that DCS isn't fully understood and all of
> > the models that computers use (and tables are based on) only claim to
> > use fairly conservative assumptions about a "normal" human body?
>
> Wasn't this and related points covered in these in my initial post? :
>
> RF> "Re: Dive computer vs. Table"
> RF> 16 Jan 1995 by Reef Fish (Large Nassau Grouper) - Thread (8
> articles)
> RF> It also addresses the question of DIVE SAFETY using computers.
>
> RF> "Dive Computers and Safety"
> RF> 14 Feb 1996 by Reef Fish (Large Nassau Grouper)
>
>
> Ross > The assumed risk level is certainly low enough for me and the
> Ross > diving I do. It's also low enough for most other people once
> Ross > they grasp the logic of how to back up a computer with tables.
>
> 1. You HAVEN'T grasped the logic NOR have you found a method to back
> up a computer with tables. This part is absolutely clear based on
> what you wrote!
I've provided a perfectly clear and simple means for safely doing so,
including my detailed logic. If you have a problem with a specific
part of it, when you read the article, go ahead and point out the
error. Nospam's been trying without success for months.
> 2. Don't extrapolate your own perceived risk and erroneously
> perceived (invalidly perceived as valid) method of backup to
> situations for which your perception is DEAD WRONG, for others,
> based on nothing but knowing HOW DIVE COMPUTERS WORK!!
Knowledge of how dive computers work was nospam's issue, now resolved
to my complete satisfaction.
He can't provide a dive profile where the diver begins a 30fpm ascent
from depth where the Suunto RGBM computer indicated no deco obligation
at depth and where the same computer would indicate a missed stop when
at the surface.
If you can, I'll eat my words (and be on the phone to Suunto,
immediately).
> nonspam> Yes, sit out (at least)12 hours and dive by tables.
> I am leaving out this irrelevant part below:
> nonspam > Is Ross Bagley willing to assume financial liability when
> nonspam > his method fails?
>
> Sitting out 12 hours (or even 24 hours) MAY allow one to start fresh
> is applicable ONLY to TABLES throughout, but NOT to dive computers!!!
>
> If you understand computer algorithms, compartments, M-values etc..
> you'll realize that in a series of repetitive dives (even within a
> single day, and ALL dives are within NDL), a COMPUTER algorithm may
> NOT clear completely even after 24 hours, when there is sufficient
> loading in the slowest compartments on the last dive.
>
> Both ORCA and Uwatec computers have these LONG half-life compartments.
> A simple empirical observation in the ORCA computers is to see how
> many HOURS the divecomp will CONTINUE running (even after it has
> cleared
> "safe to fly", which often run up to 19 hours for some of my dive
> days)
> until it shows "turn me off now" (which indicates that ALL
> compartments
> are cleared), which may take ANOTHER 12 or more hours!!
>
> It's only at THAT point when one is "safe" to RE-START fresh, with
> tables or another computer, if you UNDERSTAND and believe how that is
> the CORRECT information provided by the dive computer!
At some point, this appears to me to be letting the computer make
your safety decisions for you.
If we are buddies and I have been planning our dives on tables and you
have been diving with your ORCA and we dive the same dives, are you
really saying that I'm taking undue risks when I follow the table
rules about time to fly and disregard what your computer is saying?
What if I can go back and figure out my dives actually on the table
(even though I originally planned them on the computer)? Are you
claiming that by now using the table rules and ignoring the computer
I'm being unsafe?
You seem to want to stick to one set of rules. Great. I will never
challenge someone else's decision to call a dive. If your computer
fails and you want to sit out a full day before taking up any other
diving, I'm not going to question you. But if we're buddies and both
of our computers fail, I'm going to switch to tables and go diving
while you sit on your hands for 24 hours.
> That is one reason why on ALL liveaboard diving, my dive computer
> NEVER stops running from the time I turn it on the first dive, until
> after the entire trip is finished five days later, even though there
> are plenty of occasions of surface intervals of greater than 12
> hours between days.
Well, that is how most of the things work. I can't turn mine off.
There's no "off" button on the darned thing. No real "on" button
either, for that matter.
> Ross> Personally, since I am rarely limited by the NDL's
> >
> Ross> This is a common way of diving in the recreational dive world...
> That's precisely the PROBLEM in your INVALID argument of trying to
> extrapolate your OWN experience, which is NOT APPLICABLE to the
> general framework/discussion of how dive computers work, or why it
> is IMPOSSIBLE to back up a failed computer by tables!
This is what is known as a repeated assertion and it doesn't make an
argument.
> As I said in my initial post:
>
> RF> 1. Review the threads and related topic(s) in the archives over
> RF> the past decade.
I've been in many of them for the past three years. So far, the best
comeback has been the "transient" deco obligation that some computers
get when you ride the ragged edge of the NDL during the ascent.
So there are some computer models such that the rounding errors cause
a momentary stop to appear while you're ascending. I just can't get
my panties in a twist over this one. It simply doesn't matter to my
risk calculation.
Even if there was an indicated deco obligation during the ascent
(which would be enough for me to sell that computer immediately), as
long as it cleared by the time I reached the surface... I'll still
treat that dive as being within the NDL's.
> RF> 2. Read a few books and scientific literature about dive computers
I know more than enough about dive computers for recreational diving
and a fair bit beyond that. But this argument doesn't need to get
into details of how computers do their jobs.
All we need to know is that dive computers (with all of their
variations) and dive tables are attempts to protect us from the same
condition: DCS. If one model in that set doesn't think you should be
bent, the others shouldn't be far off.
From there, we hit the one detail needed to make this approach safer
than diving on tables from the start (conservatism). In order to make
certain that the tables are more conservative than the computer (which
you were using until it failed), use the most conservative pressure
group on the table.
And go diving.
You are of course aware that PADI publishes a much riskier method for
changing from a dive computer monitored dive to the Wheel RDP, right?
You need to be on the warpath against PADI long before you get upset
at me for my highly conservative approach.
Ross Bagley
> Ross Bagley wrote:
> >
> > nos...@all.please.net writes:
> >
> > > In <l5cwuou...@panix2.panix.com> Ross Bagley wrote:
> > > > nos...@all.please.net writes:
> > > > > "Ross Bagley" ro...@rossbagley.com writes:
> > > >
> > > > [...snip...]
> > > >
> > > That's what my dive computer is marketed to accomplish and what I
> > > bought it for. When the computer indicates that I can do a direct
> > > ascent (when the computer indicates no decompression obligation), I
> > > feel quite safe in doing a direct ascent to the surface.
> >
> > So, are you prepared to come up with a dive that you can profile with
> > the RGBM model where the model puts the diver within the NDL's until
> > some point during a 30 foot per minute final ascent where the model
> > suddently requires a stop?
> This assumes that you are placing complete and total trust in the model
> used to calculate the deco status.
The number of reported undeserved hits on computers considerably more
liberal than Suunto's RGBM computers is low enough that I feel quite
confident trusting the RGBM model.
Though, the way I dive, I rarely push it.
> There are models out there that I am not comfortable using without
> adding quite a bit of coservitism. Any serious dive, I plan using at
> least two differing models to do a sanity check on the profile. I
> use my computer as a 'OH SHIT' bailout for any serious dives I
> do. Now here's the next question: What model does you computer
> actually use?
Suunto Cobra. Identical pressure sensor and algorithm as the Vyper,
Mosquito, Stinger, and Vytec (on the default setting). First dive is
about as liberal as most other computers, subsequent dives are more
conservative than most other computers.
[...snip planned and actual dive plan...]
> During this dive, my computer told me that when I hit 70ft, 17 minutes
> into the dive, I could go straight to the surface. Do you really want to
> test your computers model on your actual body by using it to plan your
> dives?
It sounds like you used another system to plan your dive and you stuck
to your plan. Sounds like a good idea to me.
My dive plan is normally more like: I'll be in the middle of the rig
or downcurrent of the rig between 50 and 80 fsw until I have ~20cf of
gas (in an Al S80, this is 750psi) at which point, I'll finish
whatever I'm doing and ascend. If, by some chance, I stay deep for
most of the dive and I run into the NDL before I run out of gas, I'll
ascend at that point and avoid an indicated deco obligation.
Should my computer fail during one of these dives, I'll slowly ascend,
do a safety stop where I marked 15 feet on my descent (there's usually
a structural element around that depth which is easy to find again),
get back on the boat, replace the computer with an SPG, switch to
tables (probably pressure group 'Z'), eat something, and then get my
ass back in the water.
Without any fear that I'm inviting DCS by backing my computer up with
tables. And I'm a heck of a lot more risk averse than most people I
see.
Shawn Willden
Can you explain it for us? I'd like to understand.
--
Shawn
Never trust a humble mathematician.
PADI AOW w/38 logged dives (20 ocean, 17 fresh, 1 other)
Total bottom time: 19 hours 54 minutes
Last Dive: SE shore of Fish Lake, Utah (elev. 8700), 9/1/02
Shawn Willden
> If I said I didn't dive
> any deeper than 30' I'd bet I could prescribe a foolproof method of
> computer-less safe diving: "dive as long as you want without exceeding 30'
> and you'll live."
According to GAP, you can incur a deco obligation at 30 feet. You'd need
enough gas to stay down for thirteen hours, though...
--
Shawn
Never attribute to malice that which can be adequately explained by
stupidity.
Rich Lockyer
Fish) wrote:
>Before I went out of town a few days ago, I was in the midst of an
>exchange with Matthias Voss, in which he was running around in circles
>so much that he forgot where HE started from one post to the next!
>
>So, I'll pick it up from there, and make this a GENERAL post,
>
> "You CANNOT Backup a Broken Computer by Tables",
While certainly less than optimal, you can always remember that you
aren't bent, therefore are somewhere on the table.
The most conservative shot would be to consider yourself a "Z" diver
(on the PADI table) and calculate repetitives from there.
Less than optimal, but it won't cost you a day and a half of your
liveaboard time.
--- Rich
http://richlockyer.tripod.com/
Lee Bell
> > Careful, you're about to be called names. That's the method Bob's been
> > calling Bullshit for years. In fact, there is a risk to it, but it's
not
> > yet quantified. The risk is that there is a profile that a diver might
> > reasonably have done, that will result in him having no deco obligation
at
> > the beginning of the dive, but having one by the time he reaches the
> > surface.
>
> Not with a 30fpm ascent from a dive within the RGBM model NDL's.
That was my contention as well. Since then, I've seen one profile that I
have not yet tested, than will probably have the results I described. It's
not something a diver is likely to do.
> Exactly. But I haven't bought my second Suunto yet, so my backup plan
> is to accept the reduced bottom time and fall back to tables.
That's not my plan. I have a backup computer, but if it were not along, my
plan in most circumstances would be to sit out until I could go back onto a
computer again. Until Bullshark repeats his method for me, one that I don't
seem to be able to remember, but which I have confirmed works, I'll
sacrifice some diving today to get the full time available tomorrow . . .
usually.
> I have yet to spend $1000 on a dive trip, though I understand your
> point. For the next 6 months or so, it's unlikely that I will spend
> more than $20/dive for any diving that I might do, what with needing
> all of my money to start up another business...
I've yet to spend $1,000 on a computer. As a matter of fact, I didn't pay
much more than $1,000 for all 5 computers I own combined.
Lee
Reef Fish
You have already failed!
You have once again missed the point that DIVE COMP and TABLES don't mix.
Each has its own basis for contruction and use, and there is no known
"equivalent" -- that's why you can't back one up by the other. You
back TABLES up by TABLES, and dive computers by dive computers,
preferably one that runs the IDENTICAL algorithm.
Simple. End of story.
Unless of course you can SHOW us a publication that shows that the RDP
group Z is "equivalent" to ALL dive profiles that fit the series of
dives I gave. You know no such exists, don't you?
> See? Quite simple. There's really nothing to it.
Sure. Ignorance is bliss too. And some divers DIE blissfully
without knowing why.
-- Bob.
Ross Bagley
> You have already failed!
Opinion. A perfectly valid opinion, and if you don't want to dive
because you're unwilling to use this strategy, I'm not gonna complain.
I'll be diving.
> You have once again missed the point that DIVE COMP and TABLES don't
> mix.
Only according to the narrowest possible perspective on the two systems.
> Each has its own basis for contruction and use, and there is no known
> "equivalent"
That you are willing to acknowledge.
> -- that's why you can't back one up by the other.
I'll agree that *you* shouldn't do it, since you obviously aren't
comfortable with the issues involved.
> You back TABLES up by TABLES, and dive computers by dive computers,
> preferably one that runs the IDENTICAL algorithm.
> Simple. End of story.
Indeed. And a perfectly respectable personal decision.
> Unless of course you can SHOW us a publication that shows that the RDP
> group Z is "equivalent" to ALL dive profiles that fit the series of
> dives I gave. You know no such exists, don't you?
You're reading it here. PADI RDP pressure group 'Z' is *more
conservative* than all dive profiles within recreational limits where
a recreational dive computer would have put you at the surface with no
decompression obligation.
If you don't want to grasp this point, feel free to ignore it for
your dive planning.
> > See? Quite simple. There's really nothing to it.
>
> Sure. Ignorance is bliss too. And some divers DIE blissfully
> without knowing why.
It sounds like you'd object to planning a dive after the fact with
a table and you'd throw a fit if you saw someone doing it. I can
just see you screaming, "You dove that dive with the computer! You
can't use a table now!"
It's the same nitrogen. It's the same water. If you're not bent
(because you've been staying inside the NDL's and shallower than
recreational depths), the nitrogen in your tissues is represented by
some point on the table. Figuring out exactly which point is the
most accurate one may be impossible, so go conservative and be safe.
But it's clear that you don't want to grasp this, you just want to
retain your narrow opinion and understanding and you also want to
make nasty attacks in place of a sound argument in support of your
narrow perspective.
You have fun with that. I've explained how to back up a computer with
tables in a way which is safer than if you had started the day on
tables. You and nospam seem to have personal issues with the strategy
I've clearly laid out, but your personal reluctance won't limit my
diving or recommendations I make to others.
We may have lots to discuss on another subject, another day, but I've
made my argument clear and you haven't presented anything except
assertion.
Bye,
Ross Bagley
> Ross Bagley wrote
[...snip...]
>> Not with a 30fpm ascent from a dive within the RGBM model NDL's.
> That was my contention as well. Since then, I've seen one profile
> that I have not yet tested, than will probably have the results I
> described. It's not something a diver is likely to do.
What's the profile? From your cryptic description, I've become
morbidly curious... :)
>> Exactly. But I haven't bought my second Suunto yet, so my backup plan
>> is to accept the reduced bottom time and fall back to tables.
> That's not my plan. I have a backup computer, but if it were not
> along, my plan in most circumstances would be to sit out until I
> could go back onto a computer again. Until Bullshark repeats his
> method for me, one that I don't seem to be able to remember, but
> which I have confirmed works, I'll sacrifice some diving today to
> get the full time available tomorrow . . . usually.
When I go on a liveaboard with more than two days of diving, I'll
have a backup computer.
> > I have yet to spend $1000 on a dive trip, though I understand your
> > point. For the next 6 months or so, it's unlikely that I will spend
> > more than $20/dive for any diving that I might do, what with needing
> > all of my money to start up another business...
> I've yet to spend $1,000 on a computer. As a matter of fact, I
> didn't pay much more than $1,000 for all 5 computers I own combined.
The backup computer I want is the Suunto Vytec. $850 from DiveInn.
But it's worth it for full length diving on the second and third day
after a computer failure on the first day.
For my typical spearfishing trip on the oil rigs on the Gulf Coast,
falling back to tables simply doesn't cut into the amount of time I
can spend in the water.
Ross Bagley
> On 5 Oct 2002 20:42:22 -0700, Large_Nass...@Yahoo.com (Reef
> Fish) wrote:
>
> >Before I went out of town a few days ago, I was in the midst of an
> >exchange with Matthias Voss, in which he was running around in circles
> >so much that he forgot where HE started from one post to the next!
> >
> >So, I'll pick it up from there, and make this a GENERAL post,
> >
> > "You CANNOT Backup a Broken Computer by Tables",
>
> While certainly less than optimal, you can always remember that you
> aren't bent, therefore are somewhere on the table.
Bob disagrees with this observation. Where he disagrees with it he
doesn't make clear, but there is zero chance that he will acknowledge
the truth of it.
> The most conservative shot would be to consider yourself a "Z" diver
> (on the PADI table) and calculate repetitives from there.
>
> Less than optimal, but it won't cost you a day and a half of your
> liveaboard time.
You and I and Lee and pretty much everyone except for Bob and nospam
get this. But Bob and nospam have *decided* to not understand, so
simple and reasonable argument isn't going to convince them.
A bit of helpful advice that I just learned: your time is better spent
elsewhere.
Rob Smith
"Rich Lockyer" <rloc...@linkline.DONTSPAMME.com> wrote in message
news:3955qus7o0pgms0cc...@4ax.com...
>
> While certainly less than optimal, you can always remember that you
> aren't bent, therefore are somewhere on the table.
Does this really follow? Are you convinced that it is never possible to
exceed the tables
limits without being bent?
> The most conservative shot would be to consider yourself a "Z" diver
> (on the PADI table) and calculate repetitives from there.
Again, does this really follow? Are you *sure* that in all cases and for
all compartments the Nitrogen saturation
allowed by the computer model would not exceed the Nitogen saturation
incurred for group 'Z' on the PADI tables?
Stephen Kenney
lee...@ix.netcom.com wrote on 10/8/02 6:16 AM:
> I've yet to spend $1,000 on a computer. As a matter of fact, I didn't pay
> much more than $1,000 for all 5 computers I own combined.
>
> Lee
There's probably an even safer model coming out soon for you to buy.
Reef Fish
> Fish) wrote:
>
> >Before I went out of town a few days ago, I was in the midst of an
> >exchange with Matthias Voss, in which he was running around in circles
> >so much that he forgot where HE started from one post to the next!
> >
> >So, I'll pick it up from there, and make this a GENERAL post,
> >
> > "You CANNOT Backup a Broken Computer by Tables",
>
>
> While certainly less than optimal, you can always remember that you
> aren't bent, therefore are somewhere on the table.
Near that of a hyperbaric chamber, for the unwary.
> The most conservative shot would be to consider yourself a "Z" diver
> (on the PADI table) and calculate repetitives from there.
FAR from being the "most conservative". See my follow-up to Ross's reply.
> Less than optimal, but it won't cost you a day and a half of your
> liveaboard time.
It COULD, if you understand and trust the "accounting" of your divecomp,
if you don't have ANOTHER divecomp to back it up to continue! Which is
why on liveaboards, I usually have THREE divecomps: two identical ORCA
for air, and one Uwatec Pro for Nitrox, set to air when diving air.
Computers and Tables DON'T MIX, except for the wishful, unthinking and
unknowing divers!!
-- Bob.
Shawn Willden
The actual Dive:
>
> 7 minutes @ 47ft
> 10 minutes @ 145ft
> 2 minutes @ 70ft (50/50)
> 7 minutes @ 50ft (50/50)
> 1 minute @ 40ft (50/50)
> 1 minute @ 30ft (50/50)
> 15 minutes @ 20ft (50/50)
>
> During this dive, my computer told me that when I hit 70ft, 17 minutes
> into the dive, I could go straight to the surface. Do you really want to
> test your computers model on your actual body by using it to plan your
> dives?
Interesting. Some questions:
Do the times above include ascent/descent time? For example, you say you
hit 70' 17 minutes into the dive, does that mean that you only spend ~8
minutes at 145', since you would have taken around 1-2 minutes to ascend to
your first stop? What ascent rates did you use?
Does your computer handle switching gases? What mix did it think you were
on?
What computer do you use?
Playing around with the dive planning software I have indicates that if your
recorded times were a little bit off like, say, you started to descend to
145' at 7 minutes, took a minute to get down and two minutes to get back
up, yielding 7 minutes at 145', then your computer may have been right, at
least according to the model used by my software (Buhlmann ZHL16C).
It's possible that your computer's model *is* "good", and it just appears
"bad" because your time/depth tracking/recording is less accurate than its
is. The dive profile appears to be fairly close to the NDL, so this is a
question of "did you edge past the crisp black line that has been drawn
through the broad, fuzzy gray region"?
Your conservatism is certainly a good way to stay healthy, though.
If any of the above is stupid, keep in mind that it's coming from a newbie
diver who's only recently begun to take an academic interest in
decompression theory and who is many dives away from trying any of it
personally.
--
Shawn
Where are we going? And what's with this handbasket?
Drew A. Dunn
> > dive log and/or your memory), do it and go diving. Otherwise, put
> > yourself in the most conservative pressure group on the tables and go
> > diving (this will cut into your bottom time as compared to a backup
> > computer).
>
> every instant of a no-deco report from the computer.
Can you give an example of when a computer showed no ceiling (ie deco
obligation) and by surfacing normally you would incur a deco
obligation? If the computer shows no ceiling then I should be able to
surface normally.
Drew A. Dunn
Stephen Kenney
Large_Nass...@Yahoo.com wrote on 10/8/02 8:41 AM:
> Rich Lockyer <rloc...@linkline.DONTSPAMME.com> wrote in message
> news:<3955qus7o0pgms0cc...@4ax.com>...
>> On 5 Oct 2002 20:42:22 -0700, Large_Nass...@Yahoo.com (Reef
>> Fish) wrote:
>>
>>> Before I went out of town a few days ago, I was in the midst of an
>>> exchange with Matthias Voss, in which he was running around in circles
>>> so much that he forgot where HE started from one post to the next!
>>>
>>> So, I'll pick it up from there, and make this a GENERAL post,
>>>
>>> "You CANNOT Backup a Broken Computer by Tables",
>>
>>
>> While certainly less than optimal, you can always remember that you
>> aren't bent, therefore are somewhere on the table.
A smart diver might follow along on tables(even if they have a computer)
while filling out their log to know where they are at on a table. Serving
purpose as a double check of the computer, able to switch to tables at any
time and keeps a diver fresh in the use of such tables.
>
> Near that of a hyperbaric chamber, for the unwary.
And the unknowing.
Rob Smith
"Stephen Kenney" <sfke...@earthlink.net> wrote in message
news:B9C85821.2B78A%sfke...@earthlink.net...
>
> A smart diver might follow along on tables(even if they have a computer)
> while filling out their log to know where they are at on a table. Serving
> purpose as a double check of the computer, able to switch to tables at any
> time and keeps a diver fresh in the use of such tables.
A practice I follow ,mainly out of academic interest, but have you tried
this? If you plan your dives on tables (and dive the plan) this should work
BUT if you dive to, or near, the computer's NDL limits on typical dive
profiles you can very rapidly exceed table limits in a dive series. i.e.
you are way beyond PADI 'Z' although well within computer NDL limits. In
this case following along on tables becomes impossible. ( Impossible at
least if your hypothetical diver, being smart as quoted, uses the tables as
designed, taught and tested).
To be fair once I get to 'Z+' I do start to fudge some 'level averaging'
calculations to enable me to keep an idea of what pressure group I think I
may be at throughout the dive series. This gives me a sanity check on the
computer but would I then dive on this? No way. Trying to understand and
track your Nitrogen loading to increase your academic understanding is one
thing, to risk your health on it when cheap backup computers are available
is another thing entirely.
Mike
>
> Mike wrote:
>
> The actual Dive:
> >
> > 7 minutes @ 47ft
> > 10 minutes @ 145ft
> > 2 minutes @ 70ft (50/50)
> > 7 minutes @ 50ft (50/50)
> > 1 minute @ 40ft (50/50)
> > 1 minute @ 30ft (50/50)
> > 15 minutes @ 20ft (50/50)
> >
> > During this dive, my computer told me that when I hit 70ft, 17 minutes
> > into the dive, I could go straight to the surface. Do you really want to
> > test your computers model on your actual body by using it to plan your
> > dives?
>
> Interesting. Some questions:
>
> Do the times above include ascent/descent time? For example, you say you
> hit 70' 17 minutes into the dive, does that mean that you only spend ~8
> minutes at 145', since you would have taken around 1-2 minutes to ascend to
> your first stop? What ascent rates did you use?
The times above do include the ascent/decent for the dive. The plan
assumed an
imediate decsent and a 30ft/min ascent rate. (Which I did). As for the
actual
time at 145ish, it was between 7-8 minutes. This was very close to a
no-stop
dive by some tables, and as you see, the model I prefer calls for some
deco.
>
> Does your computer handle switching gases? What mix did it think you were
> on?
Nope, I have a genesis REACT and it does single gas and thought I was on
Air
the whole time. (I know my END was greater than 100ft so don't bother
pointing
it out). I have another similar profile I dove a few weeks ago at the
same
location with 18 minutes at 145'. The schedule I dove gave me around
30-40
minutes of deco with my first stop at 80'. The computer gave me a total
of
9 minutes of deco at 10ft.
>
> What computer do you use?
>
> Playing around with the dive planning software I have indicates that if your
> recorded times were a little bit off like, say, you started to descend to
> 145' at 7 minutes, took a minute to get down and two minutes to get back
> up, yielding 7 minutes at 145', then your computer may have been right, at
> least according to the model used by my software (Buhlmann ZHL16C).
>
> It's possible that your computer's model *is* "good", and it just appears
> "bad" because your time/depth tracking/recording is less accurate than its
> is. The dive profile appears to be fairly close to the NDL, so this is a
> question of "did you edge past the crisp black line that has been drawn
> through the broad, fuzzy gray region"?
The model the computer uses isn't bad per see but its not good for my
tastes.
I like to feel good after a dive. Until I started doing deep stops, I
didn't
feel that good after a dive. Was I bent, probably not. Was I feeling the
effects of the nitrogen loading and decompression stress, I think so. I
actually feel better after doing a dive like that described above than
I have after a recreational dive well within PADI's RDP.
My point in bringing this up is that all a computer/table/model does is
try
to apply theory to model whats happening in your body. To blindly trust
those models and theories is really nuts. I have been doing dives
progressively
deeper/longer to build up my personal knowledge of how MY body reacts to
the
profiles I dive. This is the ONLY sane way in my opinion to do these
types
of dives.
>
> Your conservatism is certainly a good way to stay healthy, though.
The goal of every dive, to survive.
Mike
Charlie Allen
"Ross Bagley:
> >
> > While certainly less than optimal, you can always remember that you
> > aren't bent, therefore are somewhere on the table.
> >
> > The most conservative shot would be to consider yourself a "Z" diver
> > (on the PADI table) and calculate repetitives from there.
> >
> > Less than optimal, but it won't cost you a day and a half of your
> > liveaboard time.
>
> You and I and Lee and pretty much everyone except for Bob and nospam
> get this. But Bob and nospam have *decided* to not understand, so
> simple and reasonable argument isn't going to convince them.
>
>
> Regards,
> Ross
There are really two discussions. One question is "What do you do if your
computer fails?". On that question I agree with you: Make some reasonable
assumptions, use the tables for guidance and keep diving. I would also look at
my buddies computer, do some extra 15' hang time, and have conservative
profiles.
The second discussion is the more theoretical one of how to relate computers and
tables.
Here I disagree with (or at least consider unproved) your assertion that;
if your computer has you in no-deco, then you are somewhere on the PADI table.
Being on the table always means you are within NDL. The inverse, " 'within
NDL' guarantees 'on the table' " is true only if the table is a perfect model
of the NDL limits. In general logic terms, both "A implies B" and "B implies
A" are both true if and only if A and B are identical.
A more verbose version of my logic is as follows:
1. I assume that if you are within table limits, then you are within NDL (or
more technically, that all compartments have N2 loading less than M0).
Similarly, if you have NDL time remaining on your computer display, then all
compartments are less than M0. To avoid other complications, I assume that
the computer and the table are based on the same model (True for my DSAT-based
Oceanic Data Plus and the PADI RDP)
2. The table _cannot_ be a perfect reflection of the model since it has
rather crude resolution/steps in time and depth; and that it is difficult, if
not impossible, to track all compartments in one table. A simple example is
that
3. If you believe both #1 and #2 above, then you should also agree that
there _might be_ conditions where the computer correctly assumes that you are
within NDL, while you are beyond the limits of the table.
I suspect (but haven't proven) that the greatest discrepancies between true NDL
status and "NDL per the table" are where the slow tissues are heavily loaded, as
from long shallow dives. Indirect evidence of this is that the PADI RDP has
some special exception handling rules for pressure groups W-Z, which you only go
into for long shallow dives. This is why I was so quick to nitpick on your
table interpretation on your earlier post to Reef Fish.
The upside on using exception rules to account for slow tissue loading is
that, for normal recreational profiles, the table can allow longer repetitive
dives, or shorter SI's.
> A bit of helpful advice that I just learned: your time is better spent
> elsewhere.
>
> Regards,
> Ross
Such as counting angels on the head of a pin?? Note that I didn't tackle
the 3rd question: OK, even if being inside NDL per computer doesn't mean you
are on the table, are you far enough off the table to matter??
Charlie Allen
chandler
follow the rules of your tables, you are bent.
--
-chandler
"Stephen Kenney" <sfke...@earthlink.net> wrote in message
news:B9C85821.2B78A%sfke...@earthlink.net...
{SNIP}> A smart diver might follow along on tables(even if they have a
Ross Bagley
[...snip...]
> 1. I assume that if you are within table limits, then you are
> within NDL (or more technically, that all compartments have N2
> loading less than M0). Similarly, if you have NDL time remaining on
> your computer display, then all compartments are less than M0. To
> avoid other complications, I assume that the computer and the table
> are based on the same model (True for my DSAT-based Oceanic Data
> Plus and the PADI RDP)
> 2. The table _cannot_ be a perfect reflection of the model since
> it has rather crude resolution/steps in time and depth; and that it
> is difficult, if not impossible, to track all compartments in one
> table. A simple example is that
> 3. If you believe both #1 and #2 above, then you should also
> agree that there _might be_ conditions where the computer correctly
> assumes that you are within NDL, while you are beyond the limits of
> the table.
Which is why the strategy states that if you cannot go back and replan
your dives on the tables, you should either 1) decide to sit out or
2) use pressure group 'Z' as a conservative estimate.
> I suspect (but haven't proven) that the greatest discrepancies
> between true NDL status and "NDL per the table" are where the slow
> tissues are heavily loaded, as from long shallow dives.
Actually, it ought to be relatively easy to go back and plan those
kinds of dives on the tables, giving you a completely accurate
table-based dive plan for your next dive. The table would probably
even let you dive those shallow dives for substantially longer than
the computer would have.
Also, there's always the option of sitting out even longer than the
RDP would indicate from presure group 'Z'. And finally, you always
have the option to sit out if you aren't comfortable with the risk of
switching to tables based on your previous dive profiles.
[...snip...]
> This is why I was so quick to nitpick on your
> table interpretation on your earlier post to Reef Fish.
I understand better now. I do stay shallow for a long time on my
dives, where shallow is 50-80 feet... :)
> The upside on using exception rules to account for slow tissue
> loading is that, for normal recreational profiles, the table can
> allow longer repetitive dives, or shorter SI's.
Exactly.
> > A bit of helpful advice that I just learned: your time is better spent
> > elsewhere.
> Such as counting angels on the head of a pin?? Note that I didn't
> tackle the 3rd question: OK, even if being inside NDL per computer
> doesn't mean you are on the table, are you far enough off the table
> to matter??
Exactly! Charlie gets it.
Reef Fish
> Large_Nass...@Yahoo.com (Reef Fish) writes:
> > > >
> > > > Okay, I'll play. This was my original problem given to Matthias Voss:
> > > >
> > > > RF> Day X. Dive 1. 199 fsw, 60 min. 90 min SIT.
> > > > RF> Dive 2. 150 fsw, 50 min. 3 hr. SIT.
> > > > RF> Dive 3. 180 fsw, 75 min. 90 min SIT.
> > > > RF> Dive 4. 120 fsw, 90 min.
> > > > RF>
> > > > RF> These are all NO DECO dives, according to my dive computer.
> > > > RF> Let's say the computer broke after Dive 3. Now let's see YOU back
> > > > RF> it up with your tables.
> > > >
> > > > For YOU, Ross, just change the 199, 150, and 180 in the first three dives
> > > > to 130, and you'll have "within recreational limits" in the conventional
> > > > sense. I am easy. :-)
> > > >
> > > > Tell us HOW you back up with tables when the computer failed, after
> > > > Dive 3
> > >
> > > For the PADI RDP, you're in pressure group 'Z' after a slow ascent
> > > from the third dive given above.
>
> > You have already failed!
>
> Opinion. A perfectly valid opinion, and if you don't want to dive
> because you're unwilling to use this strategy, I'm not gonna complain.
I'll accept that concession, but not for the reason given, but for
the reasons *I* gave, which was:
> > You have once again missed the point that DIVE COMP and TABLES don't
> > mix.
>
> Only according to the narrowest possible perspective on the two systems.
According to the ONLY valid perspective on both.
> > Each has its own basis for contruction and use, and there is no known
> > "equivalent"
>
> That you are willing to acknowledge.
What I stated if indisputable FACTS. What I've asked was for Ross to
show us an "equivalent" (if he knew of one).
Thus, in a step-by-step reasoning, I arrived at:
> > -- that's why you can't back one up by the other.
> I'll agree that *you* shouldn't do it, since you obviously aren't
> comfortable with the issues involved.
That's twisting what I had to say. I am VERY comfortable with BOTH
systems. So comfortable with them that I KNOW FOR SURE that you're
treading on thin ice to think that you can back one up with the other
without the slightest evidence of the "equivalence" of one to the
other, in the specific example cited, as well as in ALL other
situations.
One strong FALLACY of your ILLOGIC was to the tune that you KNEW I
wasn't bent after the 3rd dive, blah, blah, blah ...
So, why didn't you back up to after the FIRST dive, and assume a Z
group on your wheel, and see where you were when I was doing my 2nd,
3rd, and 4th dives?
> > You back TABLES up by TABLES, and dive computers by dive computers,
> > preferably one that runs the IDENTICAL algorithm.
>
> > Simple. End of story.
That's a declarative statement that is clear to anyone who is equally
adapt with the concepts behind TABLES ... AND ... COMPUTER.
> Indeed. And a perfectly respectable personal decision.
Thank you. But it's a decision arrived by logic and comprehension of the
TOOLS being used, filtered through the computer between the ears, which
have accumulated knowledge that would take some 40 or more years to learn
how to READ, let alone understand fully!
> > Unless of course you can SHOW us a publication that shows that the RDP
> > group Z is "equivalent" to ALL dive profiles that fit the series of
> > dives I gave. You know no such exists, don't you?
>
> You're reading it here. PADI RDP pressure group 'Z' is *more
> conservative* than all dive profiles within recreational limits where
> a recreational dive computer would have put you at the surface with no
> decompression obligation.
Then I can say unequivocally that you're NOT a scientist, nor a
prudent user of dive computers!
You have established NOTHING about the equivalence. Why don't you apply
that ILLOGIC of yours at the end of Dive 1, and see how you proceed to
Dive 2, Dive 3, and Dive 4, instead of using the COMPUTER result
(IMPROPERLY) at the end of Dive 3 as your crutch to the faulty theory
that computers can be backed up by tables!
> If you don't want to grasp this point, feel free to ignore it for
> your dive planning.
Well, now that you brought this up ... dive planning diving with
COMPUTERS is nothing like dive planning using TABLES. Didn't you
know THAT?
For my planning ... I look at the continuous scroll on my computer
before I enter to know that I have sufficient NDL time to dive a
reasonable amoung of time at reasonable depths. Then I go look for
sharks, rays, and all the wonderful flora and fauna ... CONSULTING
my dive computer every couple minutes or so to see where my dive
profile and remaining NDL time stands ... and proceed accordingly.
THAT's all the PLANNING that's required, to use the dive computer
PROPERLY, and as safely as a table diver would do whatever s/he is
constrained to do, hand-tied by a set of inadequate and obsolete
TABLES.
I can just see Ross now ... planning a dive of 40 fsw for X minues
with his wheel. And when a whale shark shows up at 80 fsw, ALL
computer divers (who hadn't planned to be at the depth) go down
(qutie safely) to see possibly the once-a-life-time event. Ross
looks at his Almighty Wheel and remembering his Z-group, stay up
mumbling he wished he had learned how to use a dive comp properly. :-)
And so it goes...
> > > See? Quite simple. There's really nothing to it.
> >
> > Sure. Ignorance is bliss too. And some divers DIE blissfully
> > without knowing why.
>
> It sounds like you'd object to planning a dive after the fact
See my preceding example. You don't NEED to plan a dive in YOUR sense,
if you rely on the appropriate info that is furnished (and continuously
updated) by your DIVE COMPUTER! That's what computer diving is all
about ... that's still another reason supporting the FACT that
You CANNOT back up a broken computer by TABLES!
> We may have lots to discuss on another subject, another day, but I've
> made my argument clear and you haven't presented anything except
> assertion.
Fair enough. The readers can decide who's making valid, reasoned
presentation/arguments and who's not.
A decade from now, I can point to this "ancient" discussion whose
TRUISM will not have changed, while another breed of table/wheel
users, will argue just invalidly as you do, because they haven't grasped
the concepts and algorithms behind the genesis of dive computers,
ENTIRELY different from those of tables!
-- Bob.
nos...@all.please.net
> nos...@all.please.net wrote:
>
> > In <l5cwuou...@panix2.panix.com> Ross Bagley wrote:
> >> nos...@all.please.net writes:
> >> > "Ross Bagley" ro...@rossbagley.com writes:
> >>
> >> [...snip...]
> >>
> >> > Prove that you can't surface with a deco obligation from every
> >> > instant of a no-deco report from the computer.
> >>
> >> That's what my dive computer is marketed to accomplish and what I
> >> bought it for. When the computer indicates that I can do a direct
> >> ascent (when the computer indicates no decompression obligation), I
> >> feel quite safe in doing a direct ascent to the surface.
> >
> > Then you clearly do not know how they work.
>
> Can you explain it for us?
I can explain some of it.
Dan Bracuk
:A smart diver might follow along on tables(even if they have a computer)
:while filling out their log to know where they are at on a table. Serving
:purpose as a double check of the computer, able to switch to tables at any
:time and keeps a diver fresh in the use of such tables.
Does not work too well when the first dive puts you off the tables.
Dan Bracuk
Toronto, Canada
All men are cremated equal.
Best of Rec.Scuba http://www.chaoticarts.com/~scuba/
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
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nos...@all.please.net
> "Charlie Allen" <charlie.al...@usa.net> writes:
>
> > "Ross Bagley" <ro...@rossbagley.com> wrote in message
>
> [...snip...]
>
> > > The PADI RDP would only allow a 6 minute dive to 120fsw after a 90
> > > minute surface interval (since your pressure group at the start of
the
> > > fourth dive is 'F'). That is reduced 10 minutes from a maximum of
16
> > > minutes by the conservative ascent pressure group on the third
dive.
>
> > It's easy to miscalculate using tables, particularly when there are
> > a bunch of exceptions buried in the fine print on the back.
>
> > While in general I agree with your computer-to-tables transition
> > procedure, a 6 minute dive to 120fsw after 90 minute SI would
> > violate the PADI/DSAT RDP in this case. The fine print says that if
> > your ending pressure group is Y or Z after any dive in a series of 3
> > or more in one day, then the minimum surface interval between each
> > dive is 3 hours.
>
> I didn't remember that little detail about the PADI RDP. Even after
> you pointed it out, if I was to use a table to back up my computer,
> I'd probably just put the ascent pressure group at 'Z' and happily
> ignore this particular detail for my next dive plan.
This just gets more hilarious with time.
Stephen Kenney
r...@no.spa.m.meadway.demon.co.uk wrote on 10/8/02 10:37 AM:
>
> "Stephen Kenney" <sfke...@earthlink.net> wrote in message
> news:B9C85821.2B78A%sfke...@earthlink.net...
>>
>> A smart diver might follow along on tables(even if they have a computer)
>> while filling out their log to know where they are at on a table. Serving
>> purpose as a double check of the computer, able to switch to tables at any
>> time and keeps a diver fresh in the use of such tables.
>
> A practice I follow ,mainly out of academic interest, but have you tried
> this? If you plan your dives on tables (and dive the plan) this should work
> BUT if you dive to, or near, the computer's NDL limits on typical dive
> profiles you can very rapidly exceed table limits in a dive series. i.e.
Well that doesn't seem right to me. Something's wrong.
> you are way beyond PADI 'Z' although well within computer NDL limits. In
> this case following along on tables becomes impossible.
They should be somewhat consistant. What's your definition of bottom time? I
believe BT is from the time of descent until you begin the ascent.
>( Impossible at
> least if your hypothetical diver, being smart as quoted, uses the tables as
> designed, taught and tested).
If you use tables with different definitions then you get far different
results.
Stephen Kenney
NOTb...@pathcom.com wrote on 10/8/02 2:14 PM:
>
> Does not work too well when the first dive puts you off the tables.
No that wouldn't work at all. What profile are you talking about?
nos...@all.please.net
> nos...@all.please.net wrote in message
> > > If you can reconstruct your dives for the day on the tables (from
your
> > > dive log and/or your memory), do it and go diving. Otherwise, put
> > > yourself in the most conservative pressure group on the tables and
go
> > > diving (this will cut into your bottom time as compared to a backup
> > > computer).
> >
> > Prove that you can't surface with a deco obligation from
> > every instant of a no-deco report from the computer.
>
> Can you give an example of when a computer showed no ceiling (ie deco
> obligation) and by surfacing normally you would incur a deco
> obligation?
To doubt the table backup method there is no need to do so.
The slower copies (compartments) of a Haldanean model
continue to on-gas during the ascent. Only the faster
copies (compartments) begin to off-gas. What's faster and
what's slower depends on the depth.
> If the computer shows no ceiling then I should be able to
> surface normally.
Put all copies (compartments) at their respective limits
and make the ascent from some depth. If some of the copies
(compartments) are over their respective limits when the
simulation hits the surface, then after the ascent any dive
history that places that copy (compartment) at or near its
limit at that depth leaves you outside the design
parameters of a table built from the same model. If this
happens, then the model is "bent," and the diver doesn't
know it since the computer failed. The diver may be bent.
The diver may be bent and hit the water again before
symptoms develop.
OTOH, a backup computer will tell you about the required
stop.
Rob Smith
> in article 3da317d1$0$8505$cc9e...@news.dial.pipex.com, Rob Smith at
> r...@no.spa.m.meadway.demon.co.uk wrote on 10/8/02 10:37 AM:
>
> >
> > "Stephen Kenney" <sfke...@earthlink.net> wrote in message
> > news:B9C85821.2B78A%sfke...@earthlink.net...
> >>
> >> A smart diver might follow along on tables(even if they have a
computer)
> >> while filling out their log to know where they are at on a table.
Serving
> >> purpose as a double check of the computer, able to switch to tables at
any
> >> time and keeps a diver fresh in the use of such tables.
> >
> > A practice I follow ,mainly out of academic interest, but have you tried
> > this? If you plan your dives on tables (and dive the plan) this should
work
> > BUT if you dive to, or near, the computer's NDL limits on typical dive
> > profiles you can very rapidly exceed table limits in a dive series.
i.e.
>
> Well that doesn't seem right to me. Something's wrong.
What doesn't seem right? Surely it is clear that if you run a multi-level
profile on computer you will get very different limits to those on tables?
However even if the profile dived happened by coincidence to exactly match
the limited profiles supported by tables you would still expect
discrepancies unless tables and computer used exactly the same model. In
fact you don't even need a series of dives to show this effect, your first
dive can be entirely within computer NDL limits at all times, even on the
'conservative' Suuntos I use, and still be way off PADI tables.
>
> > you are way beyond PADI 'Z' although well within computer NDL limits.
In
> > this case following along on tables becomes impossible.
>
> They should be somewhat consistant. What's your definition of bottom time?
I
> believe BT is from the time of descent until you begin the ascent.
This is indeed the definition I would use when working with PADI tables.
However the inconsistency isn't anything to do with bottom time definition
but mainly inconsisteny between the actual profile of a dive and the
profile you can model through tables supplemented by differences in the
saturation model used by computer and table.
>
> >( Impossible at
> > least if your hypothetical diver, being smart as quoted, uses the tables
as
> > designed, taught and tested).
>
> If you use tables with different definitions then you get far different
> results.
Indeed.
Charlie Allen
<nos...@all.please.net:
>
> Put all copies (compartments) at their respective limits
> and make the ascent from some depth. .........
No known dives or combinations of dives do this. This is NOT a reasonable
starting point.
Charlie Allen
Dan Bracuk
:No that wouldn't work at all. What profile are you talking about?
Here's a typical one - 80 4 70 on air.
nos...@all.please.net
Sure, I could build one that always has 0 displayed for
dive time remaining. Safe enough?
nos...@all.please.net
You need to read the entire post before prattling.
nos...@all.please.net
> and make the ascent from some depth. If some of the copies
+= I used "limit" in two different ways here. Sorry about that.
+ means: no decompression limit
- means: over pressure allowable at the surface.
Again, my apologies.
nos...@all.please.net
> Rich Lockyer <rloc...@linkline.DONTSPAMME.com> writes:
>
> > On 5 Oct 2002 20:42:22 -0700, Large_Nass...@Yahoo.com (Reef
> > Fish) wrote:
> >
> > >Before I went out of town a few days ago, I was in the midst of an
> > >exchange with Matthias Voss, in which he was running around in
circles
> > >so much that he forgot where HE started from one post to the next!
> > >
> > >So, I'll pick it up from there, and make this a GENERAL post,
> > >
> > > "You CANNOT Backup a Broken Computer by Tables",
> >
> > While certainly less than optimal, you can always remember that you
> > aren't bent, therefore are somewhere on the table.
>
> Bob disagrees with this observation. Where he disagrees with it he
> doesn't make clear, but there is zero chance that he will acknowledge
> the truth of it.
>
> > The most conservative shot would be to consider yourself a "Z" diver
> > (on the PADI table) and calculate repetitives from there.
> >
> > Less than optimal, but it won't cost you a day and a half of your
> > liveaboard time.
>
> You and I and Lee and pretty much everyone except for Bob and nospam
> get this. But Bob and nospam have *decided* to not understand, so
> simple and reasonable argument isn't going to convince them.
>
> A bit of helpful advice that I just learned: your time is better spent
> elsewhere.
Bob and I were understanding before you were diving.
I must bite my tongue to keep from encouraging Bagley to
test his method late in a multi dive per day / multi day
trip.
Maybe he doesn't dive that way either.
nos...@all.please.net
> On 5 Oct 2002 20:42:22 -0700, Large_Nass...@Yahoo.com (Reef
> Fish) wrote:
>
> >Before I went out of town a few days ago, I was in the midst of an
> >exchange with Matthias Voss, in which he was running around in circles
> >so much that he forgot where HE started from one post to the next!
> >
> >So, I'll pick it up from there, and make this a GENERAL post,
> >
> > "You CANNOT Backup a Broken Computer by Tables",
>
>
> While certainly less than optimal, you can always remember that you
> aren't bent, therefore are somewhere on the table.
> (on the PADI table) and calculate repetitives from there.
>
> Less than optimal, but it won't cost you a day and a half of your
> liveaboard time.
Perhaps. I've seen no guarantee.
Lee Bell
> You have once again missed the point that DIVE COMP and TABLES don't mix.
> Each has its own basis for contruction and use, and there is no known
> "equivalent" -- that's why you can't back one up by the other. You
> back TABLES up by TABLES, and dive computers by dive computers,
> preferably one that runs the IDENTICAL algorithm.
You have once again missed the point. Nobody has said that there is an
equivalent, well nobody that I'm still paying a lot of attention to. Pretty
much everybody that is knowledgeable agrees with you that there is, in fact,
no equivalent. The point others are trying to make that you seem to be
trying very hard to avoid is that, while not equivalent, there is somthing
that can be done to allow a safe dive after a computer fails. That is not
the same dive you might plan with a computer is not relevant to the fact
that you can safely plan a dive.
> Unless of course you can SHOW us a publication that shows that the RDP
> group Z is "equivalent" to ALL dive profiles that fit the series of
> dives I gave. You know no such exists, don't you?
Unless you can show something that is greater than Z, and still without deco
obligation, then it's not necessary that it be equivalent. When the ride
says you must be this tall to go, it does not mean exactly this tall.
Taller is fine. So is a repetitive dive group that is beyond what the exact
group, if there even is an exact group, is.
> Sure. Ignorance is bliss too. And some divers DIE blissfully
> without knowing why.
Many while using a computer . . . that has not failed.
Lee
nos...@all.please.net
> in article 8fb7380b.02100...@posting.google.com, Reef Fish
at
> Large_Nass...@Yahoo.com wrote on 10/8/02 8:41 AM:
>
> > Rich Lockyer <rloc...@linkline.DONTSPAMME.com> wrote in message
> > news:<3955qus7o0pgms0cc...@4ax.com>...
> >> On 5 Oct 2002 20:42:22 -0700, Large_Nass...@Yahoo.com (Reef
> >> Fish) wrote:
> >>
> >>> Before I went out of town a few days ago, I was in the midst of an
> >>> exchange with Matthias Voss, in which he was running around in
circles
> >>> so much that he forgot where HE started from one post to the next!
> >>>
> >>> So, I'll pick it up from there, and make this a GENERAL post,
> >>>
> >>> "You CANNOT Backup a Broken Computer by Tables",
> >>
> >>
> >> While certainly less than optimal, you can always remember that you
> >> aren't bent, therefore are somewhere on the table.
>
> A smart diver might follow along on tables(even if they have a
computer)
> while filling out their log to know where they are at on a table.
Serving
> purpose as a double check of the computer, able to switch to tables at
any
> time and keeps a diver fresh in the use of such tables.
My first computer dive went way beyond the table limits for
a similar dive. If you think the tables can be used in a
fashion other than that posed by the table maker, then why
didn't the table maker propose such a method? (PADI
excepted of course.)
Lee Bell
> > Each has its own basis for contruction and use, and there is no known
> > "equivalent"
>
> That you are willing to acknowledge.
There's no known decimal equivalent for 1/3, but there doesn't need to be
for me to know that it's less than Z . . . I mean one.
Lee
Charlie Allen
<nos...@all.please.net wrote:
"Charlie
> Allen" wrote:
> >
> > <nos...@all.please.net:
> >
> > >
> > > Put all copies (compartments) at their respective limits
> > > and make the ascent from some depth. .........
> >
> >
> > No known dives or combinations of dives do this. This is NOT a
> reasonable
> > starting point.
> >
> > Charlie Allen
>
> You need to read the entire post before prattling.
>
>
I did read your entire post. I also read the entire post copied above, but
couldn't find where defended your erroneous starting point.
Charlie Allen
Lee Bell
> Being on the table always means you are within NDL. The inverse, "
'within
> NDL' guarantees 'on the table' " is true only if the table is a perfect
model
> of the NDL limits. In general logic terms, both "A implies B" and "B
implies
> A" are both true if and only if A and B are identical.
Actually, what needs to be true for any of this discussion is that when the
computer says you are OK, you are and that when the tables say you are OK,
you are. Neither is, of course, strictly true, but it's a premise we have
to accept, plus or minus whatever additional conservatism we chose to
employ.
I, for example am a bit anal about surfacing when my computer is in it's
yellow caution zone. I much prefer to begin my ascent before I enter that
caution zone or, when I'm willing to risk some decompression time, to use
deep and progressively shallower stops to bring my apparent loading into the
zone my computer shows as safe. On a dive I don't plan for deco, like the
ones Mike, Ryan and I did on Sunday, I'm just a bit more certain that a
computer failure, followed by my normal ascent, puts me somewhere within the
table's useful range, even if I don't quite know where in that range it is.
> The table _cannot_ be a perfect reflection of the model since it has
> rather crude resolution/steps in time and depth; and that it is difficult,
if
> not impossible, to track all compartments in one table.
Just as an unmarked yard long stick is a cruder measure of a few inches than
a foot long one, but you still know that the actual distance is less than a
yard.
Lee
Lee Bell
> > While certainly less than optimal, you can always remember that you
> > aren't bent, therefore are somewhere on the table.
Don't I just wish this was true. Sometimes being bent doesn't show up for a
while . . . like a couple of dives after the damage is done.
Lee
nos...@all.please.net
> Ross Bagley wrote
>
> > > Each has its own basis for contruction and use, and there is no
known
> > > "equivalent"
> >
> > That you are willing to acknowledge.
>
> There's no known decimal equivalent for 1/3,
_
0.3 = 1/3 (and I mean exactly)
> , but there doesn't need to be
> for me to know that it's less than Z . . . I mean one.
I don't know what this means.
nos...@all.please.net
> Reef Fish wrote
> > Sure. Ignorance is bliss too. And some divers DIE blissfully
> > without knowing why.
>
> Many while using a computer . . . that has not failed.
How many?
Proportionally, how many compared to tables?
I'm willing to go with a rational time adjustment...
How many?
Check it out, there is a reason you don't see any computer
implementations of tables. What is it?
nos...@all.please.net
You are then necessarily ill equipped to continue...
nos...@all.please.net
Experience is telling isn't it?
Bob Crownfield
you need to understand what you are talking about before you prattle.
nos...@all.please.net
> Greg Mossman wrote:
>
> > If I said I didn't dive
> > any deeper than 30' I'd bet I could prescribe a foolproof method of
> > computer-less safe diving: "dive as long as you want without
exceeding 30'
> > and you'll live."
>
> According to GAP, you can incur a deco obligation at 30 feet. You'd
need
> enough gas to stay down for thirteen hours, though...
I've read that people have been bent after diving toa max depth of 18ft.
I have a dive computer that can incur a 1ft deco stop.
Roll the dice and live with it.
Ross Bagley
Any multilevel dive that starts deep and spends a lot of time shallow.
Since the table gives you no credit for coming shallow and treats the
entire dive as if you were at the max depth, it's remarkably easy to
do a dive on Devil's Throat, in Cozumel, for instance, where the max
depth during the dive is 120fsw, but you spent 40 minutes exploring the
wall.
Regards,
Ross
-- Ross Bagley http://rossbagley.com/rba
"Security is mostly a superstition. It does not exist in nature...
Life is either a daring adventure or nothing." -- Helen Keller
Ross Bagley
What's really funny is that you're looking for one.
Did you get a guarantee with your computer? Did PADI (or whichever
agency it was) give you a guarantee about your safety using their
dive planning techniques?
Do you understand what risk really is? Do you understand how to
evaluate two risks to determine if they are equivalent or if one of
them is more important?
From your posting history, it looks like you've got some serious
learning to do before you're qualified to carry on this discussion.
I suggest you get to it. You're not getting any younger.
Stephen Kenney
NOTb...@pathcom.com wrote on 10/8/02 5:58 PM:
> From Stephen Kenney
> :No that wouldn't work at all. What profile are you talking about?
>
> Here's a typical one - 80 4 70 on air.
>
What the hell does that mean?
Stephen Kenney
r...@no.spa.m.meadway.demon.co.uk wrote on 10/8/02 5:47 PM:
> In
> fact you don't even need a series of dives to show this effect, your first
> dive can be entirely within computer NDL limits at all times, even on the
> 'conservative' Suuntos I use, and still be way off PADI tables.
Describe the profile that backs up your claim.
Stephen Kenney
ro...@rossbagley.com wrote on 10/8/02 10:36 PM:
> Stephen Kenney <sfke...@earthlink.net> writes:
>
>> in article 3da34a8d...@news.axxent.ca, Dan Bracuk at
>> NOTb...@pathcom.com wrote on 10/8/02 2:14 PM:
>>
>>>
>>> Does not work too well when the first dive puts you off the tables.
>
>> No that wouldn't work at all. What profile are you talking about?
>
> Any multilevel dive that starts deep and spends a lot of time shallow.
>
> Since the table gives you no credit for coming shallow and treats the
> entire dive as if you were at the max depth,
If you treat the entire dive at max depth then the tables are worthless.
Computers give you credit for time spent shallow and average the NDL why not
do the same with tables?
Reef Fish
> In <ao03nh$suv$1...@slb2.atl.mindspring.net> "Lee Bell" wrote:
> >
> > There's no known decimal equivalent for 1/3,
>
> The following is best viewed in a fixed pitch font:
> _
> 0.3 = 1/3 (and I mean exactly)
Ask Lee what a LINEAR function is! :-) He argued till his face turned
BLUE that 1/X is a LINEAR function. And he didn't know why he was called
an idiot on those occasions. :-))
And he WHINES about it. And he CLAIMS he has won the debate because
he was called an IDIOT. BHAHAHAHAHAHAHAHA.
********** Folks, THAT's the Genesis of Lee's Rule!!! ************
>
> > , but there doesn't need to be
> > for me to know that it's less than Z . . . I mean one.
>
> I don't know what this means.
Nobody does, except Lee, when he is talking gibberish, and that includes
just about EVERYTHING related to mathematics, statistics, and physics.
The archives are littered with gems by Lee on those subjects.
-- Bob.
Reef Fish
> Reef Fish wrote
>
> > You have once again missed the point that DIVE COMP and TABLES don't mix.
> > Each has its own basis for contruction and use, and there is no known
> > "equivalent" -- that's why you can't back one up by the other. You
> > back TABLES up by TABLES, and dive computers by dive computers,
> > preferably one that runs the IDENTICAL algorithm.
>
> You have once again missed the point. Nobody has said that there is an
> equivalent, well nobody that I'm still paying a lot of attention to. Pretty
> much everybody that is knowledgeable agrees with you that there is, in fact,
> no equivalent.
Then it follows that you CANNOT backup one by the other, in the sense
that you can BACKUP a computer by a computer, or a table by a table,
because they are "equivalent" (and consistent) in terms of the theory
and methodology of monitoring a series of dives under decompression
theory.
TRYING to pretend that you can "backup" a computer by tables (or vice
versa) is taking such a leap of faith WITHOUT any valid basis that it
renders the monitoring of remaining dives (for safety) strictly a
matter of crapshoot or playing a Russian roulette.
> there is somthing
> that can be done to allow a safe dive after a computer fails.
Like sitting out 12 hours, 24 hours, 36 hours ... (though I've heard
only the first two mentioned in this thread; whereas 36 may be
NECESSARY to continue a long series of repetitive dives). I don't
consider that a "backup" in the sense of the present discussion.
It's an age-old "fall back plan". Hardly a "backup" when a computer
fails, as another identical computer would "backup" and enable one
to continue without interruption and fudging ad infinitum.
THAT's what you and the rest of the Tables followers failed to
understand, and MISSED the point of what constitutes a "backup", and
one that can be done "safely" only in the sense of being CONSISTENT
and EQUIVALENT to the instrument being used at the time of failure.
Read a few books about computers and decompression physiology as I had
suggested in my initial post, and come back to discuss when you have
grasped those BASIC printiples.
-- Bob.
Lee Bell
> Since the table gives you no credit for coming shallow and treats the
> entire dive as if you were at the max depth, it's remarkably easy to
> do a dive on Devil's Throat, in Cozumel, for instance, where the max
> depth during the dive is 120fsw, but you spent 40 minutes exploring the
> wall.
Or Bob's 200 foot dive for a total time of about an hour.
Rob Smith
"Stephen Kenney" <sfke...@earthlink.net> wrote in message
news:B9C91B6F.2B865%sfke...@earthlink.net...
OK, here is a dive I did a few weeks ago on Thistlegorm in the Red Sea.
This was the first dive of the day, in a multi day series, but having only
dived gently the day before we can assume essentially no tissue loading at
the start of the dive. I did this dive on EANX32 and entirely within NDL.
My buddy maintained close station on me hence having a very similar profile,
he was on air and also within NDL, if we want to quibble about minute
differences I could ask for his exact profile.
Max depth was 29.3 metres giving a maximum time before ascent (on air) of
20 minutes. I started my ascent 31 minutes into the dive which would not
have been possible on (properly used) PADI tables. Please note that I have
picked an example dive which is the most favourable for your point of view
in diving to 29.3m which the PADI tables model at 30m. I could have picked
a dive using say 25.5m which PADI tables would also have to model at 30m
giving even more extreme results.
The following profile shows sample period, each of 20 seconds, and depth in
metres at that time. Apologies to everyone else here for creating such a
long post by putting the detail in.
1 2.7
2 4
3 5.2
4 5.5
5 6.4
6 7.3
7 8.2
8 9.4
9 11
10 12.8
11 14.6
12 17.1
13 17.7
14 17.7
15 16.5
16 16.5
17 14.9
18 18.6
19 18.9
20 20.1
21 20.7
22 20.7
23 21.3
24 21.9
25 21.9
26 22.6
27 24.7
28 25
29 25
30 25
31 24.7
32 24.7
33 25.3
34 26.5
35 26.8
36 25.3
37 24.7
38 25.3
39 26.8
40 26.5
41 26.8
42 28
43 28.3
44 29.3
45 29.3
46 29
47 28.3
48 27.7
49 27.4
50 25.9
51 23.8
52 23.5
53 24.7
54 25.3
55 24.7
56 25.3
57 24.4
58 22.6
59 22.3
60 19.2
61 18.3
62 18.3
63 18
64 18
65 18.3
66 18.3
67 18.3
68 18
69 17.4
70 17.1
71 17.4
72 16.2
73 17.1
74 17.1
75 16.5
76 16.2
77 15.2
78 12.8
79 13.4
80 13.4
81 13.1
82 13.4
83 14.3
84 14.6
85 14.6
86 15.2
87 15.5
88 14.6
89 15.2
90 15.5
91 15.8
92 15.5
93 15.8
94 16.2
95 15.5
96 15.2
97 14
98 11.9
99 8.2
100 5.8
101 4.6
102 4.6
103 4.3
104 4.3
105 4
106 4
107 4
108 3.7
109 4.3
110 4.3
Lee Bell
> And he WHINES about it. And he CLAIMS he has won the debate because
> he was called an IDIOT. BHAHAHAHAHAHAHAHA.
No, I claimed you lost. Different.
Lee Bell
> > > > While certainly less than optimal, you can always remember that you
> > > > aren't bent, therefore are somewhere on the table.
> >
> > Don't I just wish this was true. Sometimes being bent doesn't show up
> for a
> > while . . . like a couple of dives after the damage is done.
>
> Experience is telling isn't it?
Yes, it is.
Lee Bell
> > You have once again missed the point. Nobody has said that there is an
> > equivalent, well nobody that I'm still paying a lot of attention to.
Pretty
> > much everybody that is knowledgeable agrees with you that there is, in
fact,
> > no equivalent.
>
> Then it follows that you CANNOT backup one by the other, in the sense
> that you can BACKUP a computer by a computer, or a table by a table,
> because they are "equivalent" (and consistent) in terms of the theory
> and methodology of monitoring a series of dives under decompression
> theory.
No, it does not follow, at least not in the sense that everybody but you is
discussing. You do not need to have equivalence, you just need sufficiency.
If you have two computers, one more conservative than the other and are
diving according to the less conservative one (note I did not say to its
limits) when it goes out. If the more conservative one still says you're
OK, then you can continue diving with it, right? No equivalent, but it's
still OK. Same thing for the tables. The next dive will not be the same as
it might have been with the computer functioning, but it can still happen.
That's all most of us are and have been saying and you know it.
Lee Bell
> My first computer dive went way beyond the table limits for
> a similar dive. If you think the tables can be used in a
> fashion other than that posed by the table maker, then why
> didn't the table maker propose such a method? (PADI
> excepted of course.)
Perhaps because those that designed the original tables did so before dive
computers were around?
Joseph Chandler
sfke...@earthlink.net wrote on 10/9/02 2:39 AM:
> If you treat the entire dive at max depth then the tables are worthless.
No. But you would be using them as they were designed and tested. - chandler
Joseph Chandler
>
> Read a few books about computers
Are there any books about dive computers? -chandler
Shawn Willden
> In <0pf97-...@zedd.willden.org> Shawn Willden wrote:
>> nos...@all.please.net wrote:
>>
>> > In <l5cwuou...@panix2.panix.com> Ross Bagley wrote:
>> >> nos...@all.please.net writes:
>> >> > "Ross Bagley" ro...@rossbagley.com writes:
>> >>
>> >> [...snip...]
>> >>
>> >> > Prove that you can't surface with a deco obligation from every
>> >> > instant of a no-deco report from the computer.
>> >>
>> >> That's what my dive computer is marketed to accomplish and what I
>> >> bought it for. When the computer indicates that I can do a direct
>> >> ascent (when the computer indicates no decompression obligation), I
>> >> feel quite safe in doing a direct ascent to the surface.
>> >
>> > Then you clearly do not know how they work.
>>
>> Can you explain it for us?
>
> I can explain some of it.
Please do! Or references would be good. I'm willing to do the reading.
--
Shawn
The downside of being better than everyone else is that people tend to
assume you're pretentious...
PADI AOW w/38 logged dives (20 ocean, 17 fresh, 1 other)
Total bottom time: 19 hours 54 minutes
Last Dive: SE shore of Fish Lake, Utah (elev. 8700), 9/1/02
Shawn Willden
> If you treat the entire dive at max depth then the tables are worthless.
> Computers give you credit for time spent shallow and average the NDL why
> not do the same with tables?
Computers don't average the NDL.
--
Shawn
"These people will go to the lowest depths," -- Tom Cowles, spammer and
convicted thief.
Shawn Willden
> Ross Bagley wrote
>
> > > Each has its own basis for contruction and use, and there is no known
>> > "equivalent"
>>
>> That you are willing to acknowledge.
>
> There's no known decimal equivalent for 1/3,
Not true. There is exactly one decimal expansion for each rational number,
all either finite in length or consisting of a finite sequence followed by
an infinitely repeated sequence.
--
Shawn
Never trust a humble mathematician.