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<p>Hi All,</p>
Am 07.02.2017 um 09:09 schrieb Rick Walsh:<br>
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<div>On 06 Feb 2017, at 19:30, Robert Helling
<<a moz-do-not-send="true"
href="mailto:helling@atdotde.de"
target="_blank">helling@atdotde.de</a>>
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no progress report: I guessed it’s the
max_ambient_pressure but now I know, it is
not. Tonight, I will not have further time
to look into this (we have visitors), so if
someone else wants to give it a try: There
are a few other state variables of VPM-B,
all defined as global variables in deco.c. I
would next try max_crushing pressure (by
resetting this between dives and see if this
makes the deco almost independent of the
day. In Buehlmann, one can see, that the
difference in saturation is only minimal).</div>
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<div>I think I understand this now. This is a „feature“
of the VPM-B model. (For some background on this model
see <a moz-do-not-send="true"
href="http://euve10195.vserver.de/wp/?p=27"
target="_blank">http://euve10195.vserver.de/<wbr>wp/?p=27</a>
or the German version <a moz-do-not-send="true"
href="http://euve10195.vserver.de/wp/?p=46"
target="_blank">http://euve10195.<wbr>vserver.de/wp/?p=46</a>)</div>
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<div>If you are doing repetitive diving, this is tracked
between dives and since p_max (the maximal over
pressure during the dives) enters the maximal depth
encountered is relevant for the deco. Your first dive
has a depth of 60m so it sets this variable also for
the second dive which is only 40m. Thus, according to
these formulas, it allows for a bigger gradient which
means it is more liberal with respect to over pressure
in the tissues which results in shorter deco.</div>
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<div>And no, I don’t think this makes sense. But it is
the model. It is not the first oddity of this model we
come across. </div>
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<div>That quirk is indeed odd. I can see how it could have
this unexpected effect, but are you sure that's the entire
cause? I found no change at all when the surface interval
was in the range 10min to 47hr. Surely there ought to be
some variation with surface interval, even if the smaller
"crushing radius" remains.<br>
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I'm still here listening (reading) carefully ;-)<br>
<br>
I understand that we don't want to tweak the VPM-B implementation to
make the results look nicer w/o knowing if this is then still in
line with the ideas of "the real model" and I fully agree to this.
But maybe based on Linus finding there is until now really a
misunderstanding regarding the implementation for this specific
detail?<br>
<br>
<br>
There is not much I can contribute to the discussion beside one
idea:<br>
Can s.o. once check exactly the same dive scenario in another VPM-B
based tool? I heard there is another tool on the market... ;-)<br>
I unfortunately don't have a license. But I also could ask a friend
of mine. But I'm 100% sure one of you has a license.<br>
<br>
<br>
Best regards<br>
Stefan<br>
<br>
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<p>Stefan Fuchs<br>
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