CO testing

I have a Bacharach Mod 60 meter. Recently we did a test on a furnace that went to 3,800 + ppm CO , after removing the probe I let the meter run for at least 3 minutes and it would not go below 50 ppm. I took the meter outside and turned it back on. It then went to 0. I then tried retesting and the CO wet up quickly to 800+ so I stopped the test.
I then tested the Wolf range top readings such as 12, 54, 10, 176 ppm. When I tested the griddle it again wet to over 3,800 ppm CO and the meter would not go to zero when I removed the probe from the exhaust port. Again I took the meter outside to restart and it did go to 0. I then started to recheck the griddle and it also climbed very fast so I aborted the test. Next was the oven, the left side was over 700 and the right about 650 ppm. The meter did go to 0 after the oven test.
What I was concerned about was damaging the meter. The instructions indicate it will measure 2,000 ppm and calculate up to 9,999 ppm. It also indicated running the meter for 10 minutes before turning off.
Any insight or advice? The only thing I can see that I did incorrectly was not wait 10 minutes before turning the meter off.
Does anyone have any good sources on the relationship of CO, O2, CO2, stack temp etc?
Any recommendations on a class on how to tune and clean ovens and range tops.
And yes the customer was advised to immediately get his furnace, range top, griddle and over serviced before using.
Thanks Andy
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On Sat, 2 Feb 2008 22:53:00 -0800 (PST), Andy Energy

Personally, I think going outside was the correct thing to do to ensure a proper purge of the sensor...
Nasty levels of CO there, aren't there?
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has it been calibrated in the last year ?

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