User manual update: Heat map

[Rick Walsh]

Hi Robert,

On 24 Oct 2016 05:43, "Willem Ferguson" <willemferguson at zoology.up.ac.za>
wrote:
>
> I refer to my last mail on the above topic, including the altered diagram
that originated from Rick.
> Question: In Rick's diagram (as subsequently used by me) the yellow zone
appears pretty narrow. Does this reflect Rick's patch that made the yellow
zone wider?
> Kind regards,
> willem
>

Yes, that diagram does reflect the widened yellow section. I agree it still
isn't particularly wide, but it looks ok to me. Compare it to the unscaled
hue graphic at the top of this page. We're looking at 0-120deg (red to
green), so cover the rest. You'll see yellow covers a very narrow range
compared to red and green.
https://en.m.wikipedia.org/wiki/Hue

I really only stretched the yellow zone towards green, rather than towards
red. Even though it looks like lots of red in the scale diagram, that goes
well above gf100. If you conside that few people (at least that I'm aware
of) would dive with gf >85, the heatmap still has very little red when
looking at real dives.

I like changing the annotation lines to blue.  I don't mind which way
around the colour scale and bar graph are.  Overall I think the updated
graphic looks good, but the ongas/offgas boundary needs to go back to the
point of inert gas equilibrium/saturation  (i.e. black on scale).

On 23 Oct 2016 03:36, "Lita Ferguson" <ferguson.lita at gmail.com> wrote:
>
> Here is a rearrangement of your diagram that is possibly more logical if
one starts the explanation of the heat map by refering to the gas pressure
graph. A few points:
>
> 1) The ranges for offgassing and ongassing on the righthand side need to
be demarcated at the light green zone (0% of M-value). If the demarcation
corresponds to the black zone (100% inert gas equil pressure) then there
needs to be an explanation of for the colours between black (100% inert gas
equil pressure) and light green (ambient pressure).
>
Inert gas saturation occurs when there is equilibrium between the tissue
and breathed gas partial pressure. That is at 100% inert gas equilibrium
pressure. Below this point the tissue is under-saturated and ongassing;
above this point the tissue is over-saturated and offgassing.

This is why breathing gas with high fraction (or pure) oxygen is so
efficient for decompression.  The diver can offgas rapidly while
maintaining a relatively low (even zero is theoretically possible) gradient.

> 2) I omitted the word Bühlmann from the lable "M-value" because this ties
the diagram very solidly to the Bühlmann algorithm and not to the VPM-B
model.
>

I deliberately included "Bühlmann" to make it clear that the colours are
relative to Bühlmann's M value, regardless of the chosen deco model or
conservatism (to facilitate comparison of different dives and plans). The
only reason to omit "Bühlmann" would be because the M value only relates to
the Bühlmann model, so it can be assumed without being explicitly stated.
If this is the case, then it should be explained in the text.

> 3) I added % symbols to the scale values on the right of my version of
the diagram in order to make the captions e.g '% of inert gas equilibrium
pressure" more immediately understandable.
>
I like this change.

> A question from a naïve diver who knows nothing about the VPM-B
calculations. In which way is the M-value part of the VPM-B algorithm? In
other words, does it depart from a Bühlmann point of view?
>
The M value plays no role in VPM-B calculations. It is used only for
comparison in the heatmap.

The M value is the maximum tolerable gradient estimated by Bühlmann. VPM-B
estimates the maximum tolerable gradient differently.

Cheers,

Rick
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