I did the same thing at my office and brought it into a conference room with 7 other people. We watched the CO2 climb to about 900 and then it started going down. Seems the climate control system is also tracking CO2 and it started pushing fresh air in when the level got too high. A nice surprise that we have systems managing this - I don't know how common that is in offices though.
Anecdotal, but I used to work in an IT department where some areas had good, or at least tolerable, ventilation and some very clearly did not. The difference in moods and productivity between teams in each was distinct enough to notice, but, at the time, I don't think anyone would have thought of CO2 levels as a confounding issue.
