dealing with unused tanks

[Jef Driesen]

On 29-12-12 07:57, Dirk Hohndel wrote:
> Jef Driesen <jefdriesen at telenet.be> writes:
>> I believe some Oceanics even have a feature to monitor tank pressure from your
>> buddy. In that case the tank pressure has no relation with your gas mixes at
>> all. I don't think I have ever seen data from such a device.
>
> The Uemis can do that, too, but looking at their file format I don't
> think they store that data. Once I finally have the second tank sensor
> Linus and I can test the various scenarios...

All device with a wireless sensor can do it (assuming they have enough range to 
reach your buddy of course), but not all devices will have built-in support for 
it through some special setting.

>> If you switch tanks, you no longer get any pressure data from the previous tank.
>> Of course there might be devices that store pressure data from all sensors
>> simultaneously, but I don't think I have ever seen that so far.
>
> I'm sure that will come. With flash being so cheap and at least some
> vendors switching to reasonably fast transfer methods...

That shouldn't be a problem. Even the current api is designed to support this. 
This is one of the things I did right from the start :-)

>> Well, I think the active/inactive flag (if available) should definitely be taken
>> care of at the libdivecomputer level. I'm pretty sure everyone will agree on that.
>>
>> The used/unused part is another story. Jan already pointed out a legitimate
>> use-case where dropping unused gases would be undesirable. If we move the
>> used/unused logic into libdivecomputer, then unused gases are permanently
>> dropped, and there is no way to get them back. If it's done at the application
>> level, then the user or applications still has a choice here.
>
> Very good point. I think it would be better to have that as an
> application choice (as Jan's case clearly shows). So what I think would
> make sense is this:
>
> if you have active/inactive information, libdivecomputer could drop
> inactive tanks (unless they were switched to during the dive - which
> means that while they may have been inactive at the end of the dive,
> they were active at some point during the dive), but should report all
> other tanks, regardless of whether they were used or not. And Subsurface
> can then have a settings "show all defined gases / only used gases"
> (with the default being "only used gases" and the whole thing hidden in
> the tec preferences.

Are there any devices that allow switching to inactive gasmixes during the dive. 
That would be very counter intuitive. If the answer is yes, then what's the 
purpose of marking a gas as inactive?

I haven't tried this with the ostc.

>> So I'm not sure what's going to best way. Maybe we can treat CC dives different
>> here? I guess OC tec divers are less likely to carry "spare" mixes, only extra
>> gas volume for emergency situations. But I could be wrong on that.
>
> No, I think we should treat CC and OC the same here.

That's definitely the most consistent.

Jef