It honestly doesn’t feel like anything. I just ask my body what the number is and it’s always within a hundred ppm. it feels like a guess, but like a guess when you’ve been counting cards so long you know roughly what the count is without consciously keeping track of it? If that makes sense.

A couple of years ago, I started getting headaches. Everything in my noggin appeared normal, and one day I worked with the window open. No headache. So I got my first one, it wasn’t very expensive (€50-100 IIRC) and did some experiments. Sure enough, it would get up to 1800ppm in my tiny office and I’d get a headache.

I’d say the biggest thing it seems to affect is coding. If I can keep it below 600ppm in my office, I can code all day and late into the evening without feeling too exhausted. At about 1k, I start to feel kinda sleepy and tired after awhile.

My wife and kid had fun doing the observations and asking the questions during the experiment. Good times. We used it as a way to teach our son how to do experiments and ethics.