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PO2 settings

I wonder if abyone can clarify this a bit?
In the dive setup of PO2 there are three setting. Two are obviuous, the the PO2 warning level and the PO2 critical level.
But then there is the first PO2 setting which is the “Deko, PO2” setting. What effectc does this have? It does not say in the manual.
I have discovered that the indication of the Max Operating Depth (MOD) on the first pre-dive display is dependent on the value set of the “PO2, Deko”.
This makes sense. But is this the only impact setting this value have, to show the MOD, or are there any other dependencies? And what does it have to do with Deco?
(Sorry if this is obvious, I am a new certificae of Nitrox ????)

Top Replies

Garmin-Heath over 5 years ago +1 verified

The Deco PO2 setting served three purposes.

First, it controls at what PO2 to trigger gas switch notifications during multi-gas dives.
Second, it is the value used for multi-gas TTS calculations to project…

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0 profunditas over 5 years ago

It is assumed that deco part of the dive will have no exertion and therefore one would be able to tolerate higher pp02 to accelerate decompression. Typically 1.6 ata ppO2 for breathing pure O2 at 6m. If you don't know what it is, you shouldn't be doing it.

0 Milosherman over 5 years ago

Thanks profunditas. No, I am not going to use O2 for deco, or use deco at all..
But still, this setting of PO2 is also used to tell me the MOD at the dive start screen. And is also used in the planning mode to show me the MOD, I have discovered. Right?
The manual does not explain or mention this, so it would be good to confirm that his is the case...

0 profunditas over 5 years ago

Deco ppO2 would be used for a multi-gas dive. I don't use neither that or dive plan so can tell you theoretically only - MOD would be given for each mix. This setting does not make any sense for a single tank dive.

0 Milosherman over 5 years ago

But I think it does???
See enclosed photo of my Garmin.
The O2 is set on 32% and PO2 deco is set to 1,2. The dive selected is one gas in this case.
The MOD presented is 27 m. And this seems to directly correspond to the PO2 deco that is set to 1,2 i this case....
ciq.forums.garmin.com/.../1370129.jpg

0 profunditas over 5 years ago

OK, I've recreated the issue. Looks like an (ugly) feature. it does calculate MOD based on deco pp02 which is a semantic problem for a single gas dive. You can override it by scrolling down the menu. In reality ppO2 for deco is higher than working ppO2 so MOD would be deeper than it should be for a bottom gas / single gas This has to be designed better.

0 Milosherman over 5 years ago

Yes. And being a single gas diver only, this is also the only way to get the MOD when using nitrox.
The calculations seem right, but the parameter called ”Deko, PO2”, even with single gas chosen, seems confusing!?
And the overide by scrolling down also says ”Deko, PO2” even for a single gas...

0 Milosherman over 5 years ago

Perhaps Garmin can comment on this and explain?
How is the PO2 setting implemented and supposed to be used?
Pretty important to know I think....

0 atj777 over 5 years ago

Sounds like a very poorly named field on the Mk1.

Deco and PO2 are scarcely related. Yes, the percent of O2 in the gas you're breathing will have an affect on NDL and decompression requirements but only its effect on the N2 in the mix, and only if it's Nitrox rather than Trimix.

PO2 is important for MOD and any warnings the watch will give you as you approach the MOD. It won't and shouldn't have any affect on how the watch behaves with respect to NDL and deco. That should only be effected by the amount of N2 in the breathing gas and the depth of the dive - that's a completely separate field or fields (if also adding He).

My guess is they just mean PO2.

0 Milosherman over 5 years ago

Yes, this is how I understand it as well. Thank you for confirming atj777.
Perhaps Garmin should rename this field, if it has nothing to do with deco...?
In the Swedish version of the manual the field is called "Dekompressionspartialtryck" and explained as: "Sets the threshold of the decompression partial pressure for oxygen (PO2) in bar."
Even more confusing?

+1 Garmin-Heath over 5 years ago

The Deco PO2 setting served three purposes.

First, it controls at what PO2 to trigger gas switch notifications during multi-gas dives.
Second, it is the value used for multi-gas TTS calculations to project when a user will gas switch.
Third, it is the value used for MOD calculations in all dive modes.

We will be updating the on-device label and documentation to make that more clear.