PPO2 and CNS errors

[monkkx]

Hello,

PPO2 is calculated using EAN50 even though I've selected EAN32 for that dive. Changing the gas mix do not change the PPO2 calculation.
the CNS% is also wrong, but I assume CNS is using PPO2 or the gas mix in its formula.

On a side note, whenever I synchronise my perdix AI (in gauge mode), the gas is always set to EAN50, is there a way to set the default gas to EAN32 (or other)?

Below an example of PPO2 at 20m, with EAN32:


And the CNS is off the roof:

[nick]

Hi,

For a Perdix these values are read directly from the device - they are not calculated.

My initial thought was that this was due to gauge mode. The documentation doesn't seem to suggest anything is different though. Are you sure it's not set to EAN 50 in gauge mode on the device itself? The data format does not appear to be different in any way for gauge, so it is being interpreted as per the documentation.

And no, switching the gas in MacDive will not recalculate PPO2. That's fine for a trivial scenario only so it is done at the source.

[monkkx]

Well, a software - shearwater or macdive - only knows what it knows ... In gauge mode, Shearwater do not know what gas mix is used, hence can't calculate the ppo2 or the CNS.
When looking at the logs for the same dive on the Perdix, CNS value is N/A (not applicable).
The fact that Macdive displays a ppo2 and a CNS gave me the false impression that it was calculated based on me entering in macdive the parameters (gas mix) necessary to measure the CNS or ppo2.
So it seems that in the Perdix log file, there's a value for EANx/ppo2/CNS as per the documentation, but it's not a relevant/valid value. The software logic (shearwater or macdive) should be to NOT display the CNS/ppo2 from the log file for a gauge mode dive. But if there's an implementation for calculating the CNS/ppo2 based on the user selecting the gas mix, only then the calculated value should be displayed.
Does it makes sense?

[nick]

Yes, you're right. Sorry for the brain fart. Can you please email me your database? I don't have any gauge mode dives to test. I'll take a look at some point.

[monkkx]

Well, hold on ... I think I'm wrong
When downloading the dive using Shearwater Desktop application, it indeed display a gas mix of 50% and a CNS of 211% to 506%.

So somehow the wrong gas mix is stored somewhere in the computer, and it's not editable in gauge mode... So it seems that MacDive doesn't do anything wrong. My bad

[nick]

I think gauge mode should ignore these bits of data. I'd still like to take a look if you can send me your database (Tools > Send Database).

[monkkx]

You're right. I asked Shearwater more details on this "hiden" values but didn't get any response. Either way, yes I agree this shouldn't be displayed in gauge mode, unless it's calculated with the missing parameters entered by diver. I'll send my DB
On a side note, it would be good if there's a way to define the computer setting in the dive table (gauge, rec, tech, ...).

edit: I clicked Tools > Send DB but nothing happened, no confirmation message or anything. Let me know if you got the DB or not.