Thanks for the explanation. Alessandro
On Fri, Mar 3, 2017 at 7:30 PM, Linus Torvalds < [email protected]> wrote: > On Fri, Mar 3, 2017 at 2:59 AM, Alessandro Volpi <[email protected]> > wrote: > > > > The only remaining question is : why is the tank start pressure redundant > > field present only in a few dives, as the data are imported with > smk2ssrf ? > > I have observed that all records with the redundant data have been > generated > > by the SmartTec dive computer whilst the old Aladin Air Z O2 and the new > > Galileo Sol and Galileo Trimix are not affected. > > The reason is probably just that the SmartTec import had the dive > computer always remember and download first/last pressure data, and > then it ignores it if it's "close enough" to the sample data. > > And that's exactly what subsurface does too, except the rules for > "close enough" probably differ. > > In subsurface, the "redundancy" check is whether the samples are > within half a bar of the reported pressure (see > same_rounded_pressure() in core/dive.c - the "500" constant is because > we do things in millibar internally, of course). > > For imperial divers, that's about a 8 PSI difference where we say that > the pressures are effectively the same. > > I suspect that the SmartTec import has something similar, but maybe > the SmartTec redundancy check is tighter. Maybe it's just 0.1 bar > instead of 0.5 bar. Or, if they work natively in PSI, maybe they cut > off at 1PSI differences or something. > > As to why the dive computer would report different values to begin > with: I think your theory is right that you just turned on the dive > computer earlier, and then just test-breathing at the surface (or > temperature changes or whatever) means that the early cylinder > pressures are different from the first few samples. Or maybe the > sensor just fluctuated a bit. > > Linus >
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