On Sat, Jul 04, 2015 at 07:23:12PM +1000, Rick Walsh wrote: > I multiplied 7500 fsw by 0.304 (feet to metres) divided by 10 (metres salt > water to ata) and multipled by 1.01325 (ata to bar). > 7500 * 0.304 / 10 * 1.01353 = 231.021 bar > > It's close, but I think my conversion was very slightly out, and assumes a > certain density of salt water, which varies slightly around the world. If > I recall correctly, fsw is a "special" American unit of pressure rather > than depth. I think it is actually defined as 33 fsw = 1 ata. In which > case, to convert to bar should be: > 7500 / 33 * 1.01325 = 230.284 bar
Yes, I believe that's the right formula. BTW, Jan: if you need conversions look at what we have in units.h - and if you need something that isn't there yet, please add it there as a helper function. That makes things so much more readable, and if you do make a mistake it's easy to fix it in one spot. > We should use that number if we take 7500 fsw as the correct value. > 2301.021 vs 230.284 makes no perceivable difference to the calculated > plan. But ~230 vs 250 does. I have updated the patches anyway. > > You may be interested to see that HHS Software (V-Planner/MultiDeco) say > they use critical N2 and He radii of 0.8 and 0.7 with VPM, and 0.55 and > 0.45 with VPM-B. > https://www.hhssoftware.com/images/critrad.gif > > They have defined conservatism levels of +1, +2, +3 and +4 as increasing > the critical radii by 5%, 12%, 22%, 35%, respectively. > https://www.hhssoftware.com/v-planner-cde/faqhelp.html#config Rick, thanks for finding this information. That's extremely helpful. /D _______________________________________________ subsurface mailing list subsurface@subsurface-divelog.org http://lists.subsurface-divelog.org/cgi-bin/mailman/listinfo/subsurface
