I would like to add one other observation. My unit continues to randomly reboot – sometimes running for many hours and then entering into a phase with a number of reboots in a relative short time. The observation is that each reboot is accompanied by a downward spike in the CO2 reading. Perhaps this will be no surprise to the developers, but I find it a bit strange. The other sensors do not appear to be affected in the same way. See the attached image where I have laid the time graph onto the top of the CO2 graph.

Well – my power supply feeds two other units at the same location and they do not have problems (it is a battery-backed supply). As posted elsewhere, what is happening is that the A3 simply stops communicating over the ethernet port – even to local hosts – so nothing to do with my router. That ethernet failure apparently is in both directions so, not hearing anything coming in either, the program reboots. I have my fingers crossed now because it has run up to 410K seconds which is some kind of record for my unit….

But the topic is CO2 calibration. Update there: after about 2 weeks the A3 spontaneously decided it was time to reset the calibration so that the minimum values are about 400 PPM. This did not coincide with a reboot. I have read in another post where someone else’s unit did the something similar. I posted the month of CO2 readings so you can see what it did. The two upward steps were when I adjusted the height of the unit. No other sensor jumps coincided with the reset to 400. It was at 9:22 AM July 26. I will be watching on August 26th to see if anything interesting happens 🙂