i can recommend the CO2 monitor in the picture in that last boost. it's from Aranet4, the batteries last for months, and i've checked its readings against a properly calibrated professional CO2 monitor several times and it always agreed within 1%. now, it's quite possible that i lucked out with mine calibration wise - either way the *difference* in readings compared to outdoor baseline is what's meaningful
imagine if i cancelled the remainder of every university class i taught once the CO2 level in the classroom rose to over 1000 ppm, on the basis of that study referred to in the boost. imagine if professors banded together, equipped ourselves with CO2 sensors, and we all did cancelled class time spent above 1000 ppm. then we would get better ventilation on campus. and the students would get better learning experiences!!
I used to work in a (famous) company that has field techs with CO2 detectors on their belts, as they work in confined spaces...
...20 minutes into a team meeting, their CO2 sensors would alert 😬