There's a "backdoor" CO2 tester for $40-$50, that being a clip on your finger blood oxygen meter... the only drawback is that to check your situation, you have to fish it out of your flight bag, clip it on a finger and see how your blood oxygen is doing (as CO2 would diminish it). I have one for other reasons, but it will be in my flight bag next time out. I got mine from http:// www.semedicalsupply.com/pulse_oximeters.htm
whatever... Beach Brennan WST
