@surfingreg @jljcolorado @joeyfox Your raw number of 688 ppm CO2 is quite low considering 20 people in the room. There is math available and calculations you could conceivably do if you search the web. But, as a CO2 meter owner, my experience suggests that 688 is a very good indoor number consistent with good ventilation.
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@surfingreg @jljcolorado @joeyfox Adding 150 ppm in an hour is consistent with good ventilation as well, but check the math if you're worried. I'll find a link.
@surfingreg @jljcolorado @joeyfox https://forhealth.org/tools/co2-calculator/
(I got 777 ppm based on your data plus my assumptions at 4 changes per hour.)