Robert;
I'm unsure if you're using R22D's or not. In case you are, they should read between 9-13 mv in air. Below 9, then keep a close eye.
Whether it is another type of sensor or not, the following holds.
Divide the purity of your O2 (e.g. 97%) with the O2 purity of air and you will get a multiplication factor (e.g. .97/.209 = 4.64). Ideally, your sensors in O2 should read MVair x 4.64.
Or another way is to divide the O2 mV by the multiplication factor (make it a division factor) and see if your air mV is correct (if your actual air mV is above this number then
).
Also I have found more reliable performance by using post-dive calibrations on my Meg (sensors are calibrated in the damp state they normally operate in). The data I have posted in
http://www.rebreatherworld.com/megal...onitoring.html remains valid to this day. Hope this helps.