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

Dirk Hohndel dirk at hohndel.org
Sun Jul 5 14:42:21 PDT 2015


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.

> 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?

/D


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