I'm thinking the same thing Rob, that the meter above extrapolates the O2 reading and doesn't actually measure it.

See how I used a four syllable word there? Ha, and they said I would never amount to anything!

JHAP
~~~~~~~~~~
"My mind is a raging torrent, flooded with rivulets of thought cascading into a waterfall of creative alternatives."
...Hedley Lamarr (that's Hedley not Hedy)