On a site that uses sensors such as the Telaire 6004 in monitoring buildings, I came across this chart of the device in action...
I would presume that the room had a lower, continuous ventilation rate, and that the 'bump' is the result of a conference. It seems tantalizingly possible that from the rate of CO2 decline at the end of the meeting, that the continuous ventilation rate could be calculated. Either room size or number of people would likely be needed.
I also learned today that current Oregon code calls for CO2 monitors on each level of new construction. Hmmmmmmm..........
-AC