Fwd: Re: [PATCH] Fix up SAC calculations for ATM/bar confusion

[Dirk Hohndel]

Chris Lewis <chrislewis915 at gmail.com> writes:

>>>
>> As an example one real dive: Double7/300, pressure from 260 to 10 bar.
>> Subsurface says I used 3500 litres but Suunto Dive Manager 3176,4 litres.
>> It's a 9 % error.

But that assumes that the Suunto DM number is correct.
And I have absolutely no reason to believe that it is any better than
ours... 

>> I'd like to see some correction, but I agree using gas-mix and
>> temperature sounds too much. But, one day, someone will send a patch . . .
>
> The reality is that the temperature in the cylinder is a mystery to us.
> Sure we can assume local ambient temperature at the start of the dive
> (assuming no solar heating effects) but then what is the temperature of the
> gas in the cylinder during the dive.
> We would have to account for both cooling due to immersion of the cylinder
> in water and adiabatic effects of dropping pressure inside the cylinder.
>
> All seems more hassle than its worth. I would suggest some simple
> correction factor over a certain pressure.

But that's the fundamental problem here. There are so many moving
pieces. I am not sure we will ever get it right.

So let's assume we take whatever temperature reading we have at the time
during the dive into account, plus the non-linearity of compression. And
the mixture of gas in the tank. Is that all it takes to get the correct
volume of gas inside the tank?

/D