[PATCH 2/2] Correctly calculate SAC rate in the presense of surface events

Lutz Vieweg lvml at 5t9.de
Sun Feb 24 11:14:03 PST 2013

On 02/24/2013 07:59 PM, Linus Torvalds wrote:
> This assumes that you are not breathing your cylinders while at the
> surface, which may or may not be correct, but is usually the right
> thing.

Hmm. I would rather not speculate whether someone was breathing from
his cylinder while being at the surface.

To me it sounds more plausible to completely disregard all tank-pressure
and time measurements that were taken at the surface, and compute
SAC only from measurement periods that are known to have been spend
under the surface.

Otherwise, all kinds of funny stuff - such as testing or unintentional
free-flows, or some heavy breathing done while climbing a boat ladder
may or may not become part of the SAC calculation, depending also
on the dive computers idea of "what is surface time, how long are
samples still recorded, etc.".

> Regardless, we're better off giving a conservative (higher) SAC

In comparison to the huge SAC influencing factors that neither
Subsurface nor the dive computer nor the user can predict for future
dives, I think it would be wrong to claim that Subsurface could
actually make a "conservative" statement.
Therefore, I think reproduceability and avoidance of odd side effects
(like surface free flows) for the SAC calculation are the best that
Subsurface could offer.


Lutz Vieweg

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