Average depth and sac calculations

Dirk Hohndel dirk at hohndel.org
Tue Oct 15 09:31:47 UTC 2013


On Tue, 2013-10-15 at 09:21 -0700, Linus Torvalds wrote:
> On Tue, Oct 15, 2013 at 8:21 AM, Anton Lundin <glance at acc.umu.se> wrote:
> >
> > Both can't be right =)
> 
> Well, they *could*.
> 
> Sometimes it can be a matter of what "average depth" means. For the
> SAC rate calculations (and for dive time calculations), we ignore
> surface time. So being at the surface isn't "at depth zero" as far as
> the calculations go - it's simply not used at all. So a dive computer
> can disagree with what we calculate, because dive computers usually do
> count surface time (at least during the middle of the dive) towards
> the dive.
> 
> But in this case, you're right. What happens is that the dive doesn't
> actually have any *real* data in it at all, and all it has is:
> 
>   <depth max='13.5 m' mean='10.0 m' />
> 
> and then when we generate the *plot* for the dive, we just do the
> random fake profile (see device.c: fake_dc()). And that fake profile
> only looks at the max depth, and just does a very rough fake dive
> based on that.
> 
> So then when you measure anything from the profile, that measurement
> data is bogus, because the fake dive data is bogus.
> 
> Either you should pick a dive with real dive data, or we should fake
> the dives better when average depth data exists. Probably both.
> 
> I'll look at improving the faked dive.

In the meantime use the latest test dive I added when I didn't sleep
last night.

/D



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