Hi All, Am 07.02.2017 um 09:09 schrieb Rick Walsh: > >> On 06 Feb 2017, at 19:30, Robert Helling <[email protected] >> <mailto:[email protected]>> wrote: >> >> a 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). >> > > I think I understand this now. This is a „feature“ of the VPM-B > model. (For some background on this model see > http://euve10195.vserver.de/wp/?p=27 > <http://euve10195.vserver.de/wp/?p=27> or the German > version http://euve10195.vserver.de/wp/?p=46 > <http://euve10195.vserver.de/wp/?p=46>) > > [...] > > 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. > > 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. > > > 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. > I'm still here listening (reading) carefully ;-)
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? There is not much I can contribute to the discussion beside one idea: 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... ;-) 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. Best regards Stefan -- Stefan Fuchs E-Mail: [email protected] <mailto:[email protected]>
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