I'm not sure how accurate it is but the values seem reasonable. It hovers around 360ppm for fresh air. I can see it creep up if I'm in my office with the window

I'm not sure how accurate it is but the values seem reasonable. It hovers around 360ppm for fresh air. I can see it creep up if I'm in my office with the windows and door closed, and it spikes up if I breathe onto it.