[rogers18445]

They will apparently include calibration options in the next firmware update.

And it's not as much as of a hassle as first appears. After a week you can expect readings to drift downward by 50-200 ppm depending on whether or not you aired out the room at all - and it's a one time thing, won't happen continuously every week. Then you just take it outside and it will be fixed in under 10 minutes (<400 ppm reading trigger auto calibration immediately).

I'm not confident that the other co2 meter options are in any way better. They most likely also do auto calibration but don't tell you. Counting on the fact that most people won't notice the drift.