# [PATCH] MOD of oxygen at pO2 of 1.6 is 20ft

Rick Walsh rickmwalsh at gmail.com
Sun Jul 5 14:45:47 PDT 2015

```Hi,

On 6 Jul 2015 7:42 am, "Dirk Hohndel" <dirk at hohndel.org> wrote:
>
> On Mon, Jul 06, 2015 at 07:03:09AM +1000, Rick Walsh wrote:
> > Hi,
> >
> > On 6 Jul 2015 4:26 am, "Robert C. Helling" <helling at atdotde.de> wrote:
> > >
> > > Hi,
> > >
> > >> On 05 Jul 2015, at 15:09, Dirk Hohndel <dirk at hohndel.org> wrote:
> > >>
> > >> But what I've seen in diver training and in blender training (I'm a
> > certified trimix diver and trimix blender) is that you round to the
nearest
> > foot. Not truncate.
> > >
> >
> > Here people do that, but they also have the big semi-permanent label
> > indicating MOD down the side.  That is the depth they switch at, which
is
> > always a normal deco stop depth (multiple of 3m /10ft).  21 m (not 22 m)
> > for 50%, etc.  And the switch depth in feet is always 0.3 x the switch
> > depth in metres.
> >
> > Serious question: does anyone switch to 50% at 22m?
>
> So since we in our training style switch while swimming up the slope, we
> do tend to switch at the MOD - 20 yes, I have done gas switches at 107ft
> :-)
>
> > For the planner, we need the switch depth, not the true MOD.  Maybe we
need
> > to rename the function to something like gas_switch_depth.  Or we can
> > create a new function if the current one is used elsewhere.
>
> We already have an option to only switch gases at required decostops.
> Adding an option that limits gas switches to multiples of 10ft/3m seems
> silly, but I don't know how people are likely to use things.
>
> Obviously entering a specific gas switch depth (and using the MOD field
> for that) allows any depth a person wants - so yeah, we might rename this
> and fill in the MOD by default and tell people to overwrite that if they
> want a different depth.
>
> What do other tech divers think about that?
> > >
> > > I guess that is the best solution: Round to the nearest meter/foot
> > depending on units. Will later send a patch for this.
> > >
> >
> > To calculate switch depth, I'd be tempted to round to nearest metre.
Then
> > round down to nearest 5m.  And finally, do a psuedo conversation of 1ft
> > =0.3m to get the imperial gas switch depth.
>
> So rounding to 5m seems wrong - the typical stop depth are multiples of
> 3m/10ft. And as discussed above, I think we should not enforce things that
> don't need enforcing.

Gah. Clumbsy phone keyboard typo. I meant 3m.

>
> > I have work to go to, so won't be sending a patch in the next 12 hr.
>
> Work on Sunday the 5th... what do you do for a living?

Monday morning on this side of the Pacific. Yes, I am from the future.

>
> /D
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