[PATCH 0/3] Add best mix calculation to planner

Rick Walsh rickmwalsh at gmail.com
Mon May 23 16:13:03 PDT 2016

On 24 May 2016 at 05:19, Robert Helling <helling at atdotde.de> wrote:

> Rick,
> Am 21.05.2016 um 11:32 schrieb Rick Walsh <rickmwalsh at gmail.com>:
> I admit this isn't intuitive, and will probably only be helpful to a small
> minority of users, but it's a quick and powerful feature for those who'd
> use it, and shouldn't get in the way of anything for anyone else.
> Feedback would be most appreciated.  If this makes it into master, I'll
> write something for the manual.
> sorry for replying only now. I am just not sure this is the best user
> experience, yet.

Thanks for the response, and don't apologize; we all have plenty of other
things happening.  I'm not sold on the UI I implemented either, and hope it
can be improved too.

> The way it currently works (when the user enters something in the gas
> change depth column that ends with special character, the mix is chosen to
> be the best for that depth.
> This is good for deco gases (if somebody really wants to prescribe the
> change depth), but it does not work for the bottom mix (which for many
> would be the only mix). For that there should be a way to say „pick the
> best mix for the deepest point in the dive“. My guess would be that the
> bottom mix is the one to worry about for majority of the divers that worry
> about best mixes.

Like you, my intention / assumption was that this would only be used for
the bottom mix, and that the depth entered would be the maximum depth, or
the maximum rounded up to something considered reasonable by user.  The pO2
is based on prefs.bottompo2, not the deco gas pO2.  Part of the rationale
for using the gas switch depth field, is that the field is otherwise
insignificant for bottom mix - the planner only calculates gas switches on
ascent, so will never calculate when to switch to the bottom gas.  But I
admit that assigning a "switch depth" to a gas you don't switch to is
contradictory and not intuitive.

My initial thought was simply to have a "calculate best mix" option, but
I'm a bit wary that this could accidentally be left on by the user, and
they would end up inadvertently planning a dive with the best mix, and as
such minimal decompression, but actually diving the profile with air or
some other non-optimal mix and risking decompress sickness.  I also didn't
want to add yet another preference to already crowded the planner screen.

Another possibility:
- User can enter "best" (or "b") in either or both of the O2 and He fields
in the available gasses table (a tooltip could prompt them that they can
enter this instead of a percentage).  This is NOT automatically changed to
a percentage - most people usually enter data top to bottom and left to
right, so the gasses table would be completed before the waypoints table
and replacing the gasses with the best mix for default profile (20m?) would
not be helpful - not many people want to use EAN46 (pO2 of 1.4 at 20m) as a
bottom mix.
- Gas switch field is left blank if the user entered "best" for O2
- Gasses assigned "b" are calculated as the best mix based on the maximum
depth of the dive.  The actual mixes are displayed on the output - profile
plot and output table - but not on the available gasses table (left as

What are your thoughts?

On another point, I thought it might be worth printing below the output
table the maximum equivalent narcotic depth for any trimix dive.


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