I see. But they do have a data-logging version which is only another $40. (Although at that price, since it's only recording CO2, humidity, and temperature according to the data sheet, one might want to buy one of the other air quality sensors I listed in the QS thread; but on the gripping hand, those have persistent controversies about how accurate they really are, and you would hope that a C02 specialty site like this would be selling more accurate sensors.)