This is pretty much irrelevant though. I have a CO2 monitor for a closed space. Heavy exercise with the door closed will set off the 1500 PPM alarm every time.

This is pretty much irrelevant though. I have a CO2 monitor for a closed space. Heavy exercise with the door closed will set off the 1500 PPM alarm every time. Do I care that it is off by maybe +/- 200 PPM? Not at all. It still absolutely serves its purpose of sounding an alarm when the air gets stale.