I have been noticing that my S8 sensors tend to drift quite a lot. I’m using ESPHome, which I don’t think would affect it, but does give me an easier way to start a manual calibration, rather than wait for the Automatic Calibration to happen.
See the last 40 hours. Both Pro models have been in my basement, within 10 ft of each other and I had almost 300 ppm difference, while the Basic sensor is upstairs, closer to fresh ventilation, but not necessarily an open window.
Around 2:00 pm yesterday I moved the Pro 4.2 to outdoor for 5 minutes and kicked off a manual calibration and then brought it back to the basement, but next to my work desk so I could keep an eye on it. It had jumped over 300 ppm higher than before the calibration (although it was now in the room I directly occupied.
Today at 3:15 pm I moved the other AG Pro that was also in the basement (dark blue) outdoors, calibrated, and let sit for awhile before bringing back to the original location in the unoccupied part of the basement. Now all of them very closely match each other. Note: This particular device I self-sourced the components from Ali Express, so my S8 could be a less accurate version, or even a counterfeit for all I know.
I think they get this far off when the weekly auto calibration runs, although I don’t necessarily know it did. I may try disabling the ABC on the basement ones and see what happens.