Graph documentation [was: Re: Meaning of GF settings]

Dirk Hohndel dirk at
Tue Jan 8 12:28:47 PST 2013

Jan Schubert <Jan.Schubert at> writes:

> On 01/08/13 21:01, Linus Torvalds wrote:
>> On Tue, Jan 8, 2013 at 11:49 AM, Pierre-Yves Chibon <pingou at> wrote:
>>> Attached are the two first dives I did with my computer, the first dives
>>> of the trip as well.
>>> We did have a deco stop during the second dive (#9) but we 'only' did
>>> the safety stop 3min/3m during the first dive (#8)
>> Ok, that doesn't look horrible, and I think it's just a result of the
>> default parameters set to "somewhat conservative"
> I agree saying that it does not look that unhealthy. And there might (!)
> still be some unwanted features in the code as all of my dives using the
> dive computer generated deco also ends before the ceiling calculated by
> subsurface.

The math looks right. And your correct complaint that we don't take the
surfacing time into account when drawing the ceiling shouldn't make a
difference here, correct?

So I'm not sure what else is left. Of course, there could be bugs...

One thing to do is to look at the dives with GFlow/high 100/100. If you
still violate the ceiling, I'd start worrying :-/

>>> I used the default parameters btw (GFlow 30 and GFhigh 75).
>> If those are more conservative than even a suunto, I suspect we should
>> make them less so for the default "show" to not make people worry.
>> Then, for dive *planning* we should probably default to something very
>> conservative indeed. I dunno.
> I wouldn't do so (now) but just wait what happens to the deco
> calculations in the next days when we get more knowledge about the
> missmatchings.
> Just a note: Suunto is not using Bühlmann and GF settings at all but
> RGBM which has a little different approach and might (!) allow divers
> surface earlier than Bühlmann in case it thinks there are no
> (mentionable) bubbles in your tissues.

Linus and I have been diving together for a long time. The only time
EVER when he has shorter deco than I is if we do deep dives and my Uemis
is set to "extra careful" mode. But in all realistic scenarios it seems
that the Suunto at default settings shows shorter NDL for him.

Having written all that - we haven't spent enough times doing actual
deco dives and diving the default settings on his Suunto to make
statements about whether the total deco time that it gives us once both
computers are in deco aren't actually shorter... so you might be right
after all.


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