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<div class="moz-cite-prefix">On 10/12/2016 00:43, Robert Helling
wrote:<br>
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cite="mid:E662F1B7-BCD7-49CA-98AD-1592F978D2A0@atdotde.de"
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John,
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<div class="">Am 09.12.2016 um 22:51 schrieb John Van
Ostrand <<a moz-do-not-send="true"
href="mailto:john@vanostrand.com" class="">john@vanostrand.com</a>>:</div>
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Thu, Dec 8, 2016 at 9:36 AM, Willem Ferguson<span
class="Apple-converted-space"> </span></span><span
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class=""><<a moz-do-not-send="true"
href="mailto:willemferguson@zoology.up.ac.za"
target="_blank" class="">willemferguson@zoology.up.ac.za</a>></span><span
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<blockquote class="gmail_quote" style="font-family:
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Would it be feasible to calculate retrospective gradient
factors on real dive profiles? We sometimes use a VR3
dive computer which does give this information, but it
would be very useful to to have it being calculated
automatically for each dive.<br class="">
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class=""> Do you mean you want to see the decompression
stops for a different set of GFs? Or do you want to
automatically find the most liberal GFs that fit a dive
profile?<br class="">
<br class="">
For the former questoin set up GFs in the Preferences
and go back to view the dive. For the latter question I
iterate through GFs manually to find the closest one.</div>
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<div class="">I guess what Willem meant was to do something along
the lines we do now for VPM-B planned dives: There we compute
GFhigh/low such that you would get a similar decompression
profile.</div>
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<div class="">I have not yet answered to Willem’s original mail as
I do not really know how one would implement this. Here are my
thoughts: At each instant of time during the dive, we could
compute a gradient factor such that the current depth would be
the ceiling. That part is easy. One could then try to find a
line in the gradient factor vs depth plot that best approximates
these points. The problem is that this makes only sense during
the decompression phase of the dive, i.e. for the time where it
makes sense to consider the current depth to be at least roughly
the ceiling. During the bottom part of the dive as well as
during the first part of the ascent this would give you far too
low gradient factors.</div>
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<div class="">So we would need to find out for which part of the
dive to apply this. I don’t know what a good criterium would be:
Something like the last 25% of max depth? Some part where the
ascent is slower than the current ascent rate? We could take
user input (maybe in form of the ruler) or we could find that
last part of the dive where a linear approximation for the
gradient factor vs depth plot is best (measured in chi squared
or something similar).</div>
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<div class="">Best</div>
<div class="">Robert</div>
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<p>Yes, I was implying the interpretation that Robert gave to my
initial idea, something similar to what is calculated for dive
plans under VPM-B in Subsurface. I agree that the part of the dive
over which the FGs need to be calculated could be problematic. As
examples I attach two images of dive profiles. The first case is a
dive where GF information would really be useful. The ascent is is
clearly defined and was planned using VPM-B and GFs can be
calculated from 75% or 80% of the maximal depth. The second case
is a different type of dive (a cave dive in this case with clear
levels) that would make it very difficult to calculate GFs. But in
this case the GF information is not nearly so important as in the
first case. So if there is a lot of noise in the second case it is
not serious because there is not a ceiling that has been used as a
yard stick to determine the ascent. I suppose the possibility is
that one could use the ruler of the profile toolbar and use the
two ends of the ruler to determine the part of the dive over which
the GFs are calculated. This would make the operation user
dependent. My main point is that, for dives where the GF data
would be really useful, there is unlikely be a demarcation problem
and one could start not very far from max depth up to the point
where the surface is reached.<br>
</p>
<p>Thank you for your time an considerations.</p>
<p>Kind regards,</p>
<p>willem</p>
<p><br>
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