Meaning of GF settings (was: deco calculations)

[Dirk Hohndel]

Hi Jan...

Jan Schubert <Jan.Schubert at GMX.li> writes:
> Anyway, back to the Meaning of GF: As said, Bühlmann defines maximum
> overpressure values for all 16 tissue compartments (there are also
> easified models using "just" 8 compartments). Bühlmann itself does not
> know of GFhigh and low. If you set GFlow=GFhigh=100% then you use plain
> Bühlmann (mostly as most dive computers and calculations ad some more
> safety beside this). To add more safety to deco calculations and to
> adapt to individual preferences (like fitness, illness, coldness, ...)
> the GF limitations has been introduced meaning we just use 75% of the
> maximum overpressure defined by Bühlmann assuming you use a GFhigh=75%.
> Sidenote: The GFhigh defines the max. overpressure when surfacing, NOT
> when being/reaching/leaving the last deco stop (this is a point many
> people get wrong). To make it more complicated^Wadjustable there is an
> additional GFlow setting which defines a (usually) lower/reduced maximum
> overpressure for the beginning of the decompression phase. This also
> tries to adapt to a (disputed) deep stop based theory and heads towards
> the bubble based models in avoiding the formation of bubbles. In other
> words: GFlow and GFHigh are "just" a linear reduction of the max.
> overpressure values for all the 16 tissue compartments. The higher the
> GF settings are the shorter and shallower the deco stops but the more
> risk in getting bend. Note: GFhigh and also GFlow can be defined with
> values more than 100% if one like to use such settings.

Yes, I intentionally did not limit the gradient factors - I will however
need to add a very aggressive disclaimers to all this :-)

> And to make it even more complicated/easified there are also these 3m
> based stops introduced (10ft for imperial based people), meaning there
> is no floating deco ceiling ("smooth" using definitions by subsurface)
> but fixed stops based on depth in multiples of 3m.

As I mentioned, I wrote the planning part so that the user can define
any stops they want. So they can set 6m as their last stop. Or they can
do multiples of 5m. Etc.

> Personally I dive GFlow=30% and GFhigh=95% (which most people would
> consider quite aggressive), meaning in the beginning of the ascend I
> will not break a gradient factor of 30% (but will get a deco stop
> before) which gets linearly raised to 95% when surfacing.

I think it's the 30% that people will find aggressive, not the 95,
correct?

> Please come up with any more questions to decompression theorie (or
> medicine) if there is something not clear to you.

Thank you so much for providing more background here.

Very much appreciated.

/D