SAC and Gas Consumed Calculation

Rick Walsh rickmwalsh at
Tue Feb 11 05:39:02 UTC 2014


I have just realized that Subsurface appears to be miscalculating gas
consumption and SAC.
Gas consumption and SAC should be:
consumption = tank size x (start pressure - end pressure)
SAC = consumption / (time x (1 + ave depth / 10))

For a recent dive, Subsurface reported gas consumption as 1367 l, and
SAC as both 18.8 l/min (in dive info) and 19.0 l/min (in dive list),
yet I calculate consumption to be 1464 l and SAC to be 20.1 l/min.

Tank vol = 12.2 l (single tank entered manually in equipment)
Start 220 bar, End 100 bar (entered manually)
Ave depth = 12.8m (downloaded from DC)
Dive time = 32min (downloaded from DC)
gas consumption = 12.2 x (220 - 100) = 1464 l
SAC = 1464 / (32 x (1 + 12.2/10) = 20.1 l/min

Similar miscalculations are being made for all of my last half dozen
dives (I haven't checked the rest). Has anyone else noticed this?

I like Subsurface enough, I don't need to be flattered by it telling
me my gas consumption is better than it actually is.

I'm using Subsurface 4.0.2 on Linux mint. Binary package version
4.0.2-0exp1ppa1~raring from

I'm not a programmer, but happy to help if I can.



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