Configuration and equipment:
JJ CCR using Shearwater Petrel 3 as primary controller
Garmin Descent MK2i as backup in CCR Mode.
50 technical dives in this configuration.
On the surface, with air (21% loaded as my diluent gas), the GAS PO2 shows 0.22
Mathematically, this SHOULD read 0.21. I checked and zeroed (manually calibrated) my altimeter thinking maybe this was the issue - unresolved.
When diving in CCR mode, the PO2 of Gas is mathematically off by .01 at every depth. I took measurements comparing the Petrel 3 and the Garmin throughout the entire dive profile and it is always off by 0.01 where the Garmin is .01 higher than the Shearwater. Mathematically, the shearwater is correct and the Garmin is not.
Given that this field is a calculation based off of depth (absolute pressure at depth) and percent o2 in your diluent mix, then on the surface this should be 1 Bar x 21% = 0.21
I've checked my watch to see if there are another other settings that could affect this, but it seems like it is UNIVERSALLY off by .01 (high) so far up to depths of 50m in my testing.
Any ideas? This seems inconsequential but when diving to greater and greater depths, knowing the calculated loop PO2 is critical. With the current margin of error, this can snowball with trimix gases doing cell checks / diluent flushes at depth.
Additionally, adding this field to the FIT files might allow for further testing and resolution. I couldn't replicate from the files. The FIT file DID show an "enhanced altitude" of 79m in "user mode" and 2896m in "developer mode". Not sure why these are different or there at all given I had calibrated to zero meters altitude right before the most recent dive.
Thanks!
