On Feb 13, 2014, at 11:54 PM, Robert Helling <[email protected]> wrote:
> > On 14.02.2014, at 08:18, Jef Driesen <[email protected]> wrote: > >> If you ask me, SAC (Surface Air Consumption) defined as pressure/time is >> pretty useless because it depends on the tank volume. For example a SAC of 1 >> bar/min is equivalent to 10L/min for a 10L tank, but 15L/min for a 15L tank. >> While, SAC defined as volume/time is a truly independent number that you can >> compare across dives, regardless of the tank size. > > Totally agree. I think the source of the confusion (i.e. the idea to express > it in pressure rather than volume) is that during the dive you carry a > pressure gauge rather than a volume gauge. When you always dive with > cylinders of the same size pressure per time translates more directly to what > you see. But as soon as you dive cylinders of different size the confusion is > total. Correct. When teaching intro to tech classes this is one of the things that drives me nuts. TDI wants us to teach the students to work with the psi/min consumption and then use that in dive planning. And of course you plan both your back gas and deco gas. Back gas in our case tends to be twin 95s (err, twin 14.4l tanks), whereas the stage tank tends to be a 40cuft / 5.5l tank. And now we are back talking volumes. Just stupid. Anyway, yes, I think we’ll stick with SAC but try to add the units Patches welcome :-) /D _______________________________________________ subsurface mailing list [email protected] http://lists.hohndel.org/cgi-bin/mailman/listinfo/subsurface
