A couple years ago I bought a CO2 meter, and was astonished to see it going over 1000ppm in my office. Since then, I always keep the window cracked, keeping the CO2 levels usually under 500.
The meter was one of the best investments I ever made.
Yeah when our office got those meters it suddenly explained why I got pounding headaches after long days. I'm pretty sensitive to it apparently. I've seen it go as high as 1400 :(
Makes me wonder if the atmospheric increase from ~280ppm to the current 420ppm over the past 200 years is having some minor, but statistically significant effect on our collective cognition.
If it is, it's probably far overwhelmed by the shear weight of more well educated people and better tools at our disposal.
The meter was one of the best investments I ever made.