On Tue, Jul 18, 2017 at 2:14 PM, Dirk Hohndel <[email protected]> wrote:
> Remember, we always show the unit (l/min or cuft/min), so it's clear that SAC > isn't a pressure drop. Side note - In the mobile app, I see only "cuft", not "cuft/min". Clearly, the numbers being shown are "cuft/min" - I definitely consume more than .47cuft of air on a 49min@60ft OC dive. :) I agree that the terms are a bit fuzzy in their colloquial usage, but I do not recall SAC being used in any documentation referring to volume per time. Sure, people talk about "consumption" and sometimes improperly use the term "SAC", but people also use "good" where they should use "well" - it doesn't make it right. I was surprised to see "SAC" associated with volume per time when I started using Subsurface, but the displayed unit does make it clear what is being discussed (at least on the desktop application). The way SAC has been explained to me is that it is tank specific, but depth adjusted. This makes it useful for "how much time can I spend at X depth with Y tank?" but not for "was I breathing hard?" For that question, I've used the RMV (Respiratory Minute Volume) term, the calculation of which is neither tank nor depth specific, as it uses a volume that is normalized to the ambient pressure at depth. I've also heard RMV called SCR (Surface Consumption Rate) or SACR (Surface Air Consumption Rate or SAC Rate). For reference, the SSI definition of SAC (imperial units) is: SAC = [( PSI / T ) * 33ft] / [D + 33ft] where: PSI = Gas consumption (PSI) T = Time (min) D = Depth (ft) SAC => PSI/min This neat NAUI calculator is using a similar formula, but I couldn't find an official reference: http://www.scuba.com/scuba-gear-120/058048/NAUI-Scuba-Dive-Calculator-Surface-Air-Consumption.html I wasn't able to find an official reference for PADI, either. Here's an SDI/TDI article using the same formula: https://www.tdisdi.com/air-management-and-the-importance-of-learning-surface-air-consumption-rate-sac/ Those bodies aside, Google searches for calculating SAC seems to line up with the formula above (and its metric equivalent). > > /D > _______________________________________________ > subsurface mailing list > [email protected] > http://lists.subsurface-divelog.org/cgi-bin/mailman/listinfo/subsurface _______________________________________________ subsurface mailing list [email protected] http://lists.subsurface-divelog.org/cgi-bin/mailman/listinfo/subsurface
