# Re: User manual update: Heat map

```Hi

On 18 Oct 2016 00:27, "Robert Helling" <hell...@atdotde.de> wrote:
>
> That is, however, a different question than “what is the quality of the
decompression” that the heat-map is supposed to show: To my understanding,
the point of the Michell talk is to look at how much gas is release to the
body (potentially in the form of bubbles but who knows). And if the deco
algorithms that we use make any sense at all, the rate is determined by
looking at the difference between the inert gas pressure in the tissue and
the (total) ambient pressure (not just the ambient inert gas pressure): It
is this difference that goes into the calculation of M-values (including
gradient factors) and also goes into VPM-B in the form of the time
integral. I think, people believe that it is this number that is
proportional to the rate of forming bubbles in the body.
>
> In this sense, for example you could be off-gasing while not sourcing
bubbles, for example when breathing oxygen while the tissue pressures are
below ambient pressure.
>
Understood. My intention was to factor only the below-ambient portion of
the scale, such that the inert gas pressure line in the instantaneous bar
chart would be equivalent to black in the heatmap.
Currently the lower portion of the scale goes from cyan at zero inert gas
pressure to black at (ambient pressure * fraction inert gas in air). I
believe it would be better to make the black point equal to (ambient
pressure * fraction inert gas in breathed gas).
The (ambient pressure * inert gas pressure) to (ambient pressure) would
remain as black to green.
The green to red to white colours above ambient pressure would remain as
they are representing a percentage of the M value.```
```
Does that make sense?

> I am not saying it has to be like this (or I am convince that this is a
good description for what is actually going on in the body) but it seems to
me this is at least a (tacit) assumption of decompression models.
>
> There is another practical complication (when you want a representation
like the heat map with one value per tissue and instant of time): There is
potentially more than one inert gas. It it absolutely possible for example
that He is off-gassing while N is on-gassing (but some people argue that
this is bad for the effectiveness of decompression, they call this isobaric
counter diffusion). What are you going to plot in this situation?
>
Using the 'percentage' variable, we are considering total inert gas, and
the M value is calculated accordingly. I do not propose to change this.

Cheers,

Rick
```
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