Artifacts with VPM-B ceiling on level changes

[Robert C. Helling]

Gaetan,

> On 28 Aug 2015, at 05:31, Gaetan Bisson <bisson at archlinux.org <mailto:bisson at archlinux.org>> wrote:
> 
> I've noticed what looks to me like artifacts regarding the ceiling VPM
> calculates for multilevel dives. See the attached screenshot.
> 
> Basically, during manually entered ascent segments, the calculated
> ceiling becomes deeper as the diver goes shallower...
> 
> It might just be a well-known VPM "feature" but I still thought I would
> ask here if anyone knows what is going on.

I figured out the origin of this „feature“: The ceilings we plot are based on the allowed gradient (tissue pressure minus ambient pressure) of the tissue. This gradient is depth dependent (according to the „Boyle compensation which says that (gradient + ambient pressure)/gradient^3 must be constant during the ascent. When we plot, we use the gradient for the current depth but that shrinks as soon as we ascend and so the ceiling comes down upon the ascent. We should better plot a ceiling defined as the depth where the Boyle compensated gradient is the actual gradient and then the ceiling would no longer be depth dependent. But this requires some more work, which I have to postpone to tomorrow.

Best
Robert
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