On Tue, Apr 5, 2016 at 10:55 PM, <[email protected]> wrote: > > > > John, > > On 6 April 2016 at 12:02, John Van Ostrand <[email protected]> wrote: > >> I have an example where VPM-B +0 gives an earlier and longer deco >> obligation than VPM-B +1 and +2 for the same imported dive. I found >> another dive where +0 and +1 were almost identical. >> >> That is indeed odd; +0 should not be more conservative than +1 or +2. > Similar obligations are less surprising. > > >> I was comparing VPM-B to Cochran's algorithm on a dive were the Cochran >> gave me a minor deco obligation. To do that I'd change to the VPM-B algo in >> the Plan dive function and it would show the obligation for a dive in the >> profile display for imported dives. >> >> I'm not familiar with the Cochran. Do you know what the deco model and > conservatism you were using? > > It's using a modified Thalman. They've added bubble mechanics to it and > other modifications. It's proprietary. Conservatism is 20% on one dive and > 30% on another, Greater means more conservative. > > Personally I'm interested in how it compares but this bug report doesn't > involve the Cochran deco algo. > > >> I tried pulling out the XML for just the two dives in question but I was >> unable to duplicate the problem. When I included previous dives from the >> trip it was reproducible. It seems to be an issue when repetitive dives are >> included. The SIT was 18 hours. >> >> It sounds like it's somehow related to tissue loading from previous > dives, but I can't work out what. The VPM-B algorithm tracks tissues > mostly like Buhlmann, but there are a few funny quirks/features. > > >> I can provide an XML file to whomever is interested in investigating. The >> algo implementation is way beyond me. >> >> If you send the file to me and let me know which dives are giving the odd > results, I'll have a look when I get a chance, but don't hold your breath. > > I'll do that in the morning. > > A few questions: > > What gasses were you using? > > Ean32 in the most significant case, ean31 in another. > > Were the gas changes (if any) picked up when downloading from the DC? > > Yes. Ean32 on the entire dive. > > Does the ceiling look normal with the Buhlmann model with varying gradient > factors. > > I looked at them in the past and they looked reasonable under Bühlmann. >
For those following this. This might be a display problem more than a bug with the algo. Turning "3m incremental stops" on makes it break. So it's the 3m ceilings that appear broken not the actual ceilings. -- John Van Ostrand At large on sabbatical
_______________________________________________ subsurface mailing list [email protected] http://lists.subsurface-divelog.org/cgi-bin/mailman/listinfo/subsurface
