From: craig@cattnts.canada.ncr.com (Craig Campbell)
Newsgroups: bit.listserv.scuba-l
Subject: Re: To compute or not to compute
Date: 8 Oct 92 13:34:54 GMT
Organization: AT&T / NCR Canada Ltd., Toronto, Canada

In article <9210071709.AA05894@bent.wpd.sgi.com> story@BENT.WPD.SGI.COM ((David Duis Story)) writes:

>> Me:  I dive with a computer and love it.  I also dread the day it fails and I
>>      have to fall back to tables.

>I'm curious to see how folks plan on falling back to tables.  What's
>your plan?  Will it work midway through a week-long dive trip?

>Dave Story@bent.wpd.sgi.com           NAUI AI Z9588, PADI DM 43922, EMT

Ok, here is my theory (I've no had to do this yet, so it can't qaulify as a
method).  First, you need to know a couple of basic assumptions.

1)  If I am not in decompression mode, and can ascend, then the dive is over
   (with a safety stop), no tables required.

2)  If I don't know if I am in a decompression mode, then I must fall back to 
   my buddies computer.  The dive is not necessarily over.  That would be a 
   judgement call made at the time.

3)  Tables come into play if I am a) diving alone
			       or b) my buddy's computer also fails.

    If I was clear prior to the dive, then the dive is calculated as a straight 
    square profile dive.  Given the somewhat extreme nature of most of the
    dives I enjoy, that change in and of itself may require 'tweaking' due
    to air limitations.  (Not an action of choice.)  Because a square profile
    is more conservative than the computer, you should have 'fairly' good 
    odds of being all right, even with minor tweaking.  If tweaking is 
    necessary, however, you can't dive for 24 hours.

    If I was not clear before the dive, then I ascend to, say, 40 ft.  (Some
    depth were ongassing should be low, and where I should be level headed
    enough to do table work.  (Also, conserving my air supply has suddenly
    become of paramount importance.)  Hopefully, I noticed how far from 
    clear I were before the dive, and can recall the depth of my last
    dive.  Using my time to clear, and the maximum depth, I should be 
    able to back calculate what my repetitive dive factor was prior to
    this current (ill fated) dive.  I then use that information, along with
    my current maximum depth and bottom time to calculate my decompression
    schedule.  I cannot dive again for 24 hours.

    That is the theory.  In practice, most/all of my solo dives are done
    from a completely clear state, simply because I want to dive, and can't 
    find a buddy on short notice.  Due to geography, repetative dives are
    now rare for me, as my car simply can't carry any more tanks.  I generally
    do one extreme dive (with buddies), as opposed to several shorter dives. 

    For the few dive vacations I do go on (The Empress), I generally have a
    buddy, so I have his computer as my backup, as well as oxygen enriched
    gasses for decompression.  Thus, the computer thinks I have more nitrogen
    in my system than is actually the case both before a repetative dive, 
    and after decompression.  (As well as at the theoretical moment of 
    complete computer failure.)  This extra safety factor would give a certain
    degree of confidence in "tweaking" the table's if necessary (i.e. too
    little air for decomp...a very "bad" situation).  Or at least allows me
    to rationalize such a decision.

Well, that's basically my plan....

I still dead the day I'm forced to "fall back" to tables.

craig

    


-- 
Craig Campbell		|	These opinions are entirely the result of a 
Systems Engineer	|	small butterfly crashing into the far side
NCR Canada,		|	of the planet.  Chaos Rules.
an AT&T Company		|	I speak for no one, except, possibly, myself.
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