Low PO2 alert going off on the surface

Two more dives today.  Same thing.  

PO2 alert going off as I hit the surface, telling me to descend or switch to higher O2 gas.

Going to see if I can reset my Mk2i back to factory settings and maybe it will be fixed.  

Downside of that is that I will lose my T1 transmitter pairings, I think.  

Grrrrrr.  

Must be a bug... been through all the settings and you cannot do anything that would make this happen... that or your barometer is broken/out of whack and thinks you are diving on top of Everest? Check your baro settings and what heigh it thinks you are at at sea level. Try a recal on that and see if that helps? Not sure what else it could be other than a faulty sensor somewhere... try a reset and if still issues, back to Garmin. 

Everything else seems to be working.  Depth, NDL calculations etc. all match up with my buddy's (Cressi) computer.   Safety stop is triggering and clearing at the correct time/depth.   Altitude is reading correctly.   For some reason, when I hit the surface, my computer seems to think I'm breathing a low O2 mixture instead of regular air.  

I did a reset and reboot last night.  Hoping that this will take care of it.   If not, I guess I will have to send it to Garmin for service.  (What a pain.)   

I think I might know what's going on.  All four of these dives were done at high altitude (over 6000 feet.)  

I wonder if it's possible that this is what triggered the low PO2 alarm when I surfaced.  

Ah yes then that could be it. The Garmin uses the depth sensor when in water and barometer when in air. I guess post dive it must use the barometer. 6000 ft above sea level is 0.8 ATM which is roughly 17% air (if you compressed at sea level a full 21%). The manual does say the low po2 alarm is set to go off below 18% (0.18 po2). So this would be it I would guess. Try a sea dive and see if it happens? 

Also I would still say this is a bug as a low po2 warning shouldn't happen when surfacing, but not one to worry about. Guessing the code is using the literal po2 all the time rather than in dive po2. 

It would be great to get some suggestions from the Garmin team on whether there's a proper way to handle these types of alerts rather than just ignoring them, which I believe is bad practice. If there is a way for the device to understand that there is going to be a large differential because of the altitude of the dive, or a setting of sorts that can account for the pressure variable and give a more useful warning in these situations, that would be ideal. 

I've included my dive profile from last night for reference. It also seems to cause issues with the calculated SI time. 

Just got off the phone with Garmin dive support for this and a couple other issues (compass always about 20-30 degrees off), and they said this is a known issue with no fix and to ignore it which seems like a bad idea. 

This only happens to me at altitude (over 5000 ft) and reason is - from what was explained - there’s less O2 at altitude, so instead of surfacing with a sea level PO2, it’s reading or calculating less. So it’s accurate, but not necessary of a warning on single gas diving with air. Makes me wonder if the transmitter has an O2 sensor built in or if it’s just the algorithm guessing?

Anyways, best thing the Garmin rep suggested was to submit the idea. Silly concept, but it’s a numbers game. If enough of us complain, product team might prioritize it. 

www.garmin.com/.../

Compass is never accurate due to so many factors but handy to know if it is not playing nice.

On the PO2, the algorithm isn't guessing and no O2 sensor in the transmitter, its using your gas input as the O2 in your mix so calculating it based on the surrounding pressure. At altitude when out of the water, your atmospheric pressure is less so your PO2 is lower too (and when it drops below set % it will warn you but I assume that is lower than 18% as that is below what is considered unsafe). 5000 ft is 0.83 ATM so that's just under 18% (PO2 of 17.43) so yeah makes sense. Guess they could do something with the altitude sensor to detect this but technically your breathing air at that altitude that is less than 18% and not ideal after a dive. Get some nitrox and stick on it for a bit after your dive will help!

Guess not many people dive at such altitudes so never prioritised :(