Average depth and sac calculations

[Linus Torvalds]

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.

                Linus