My CO2 sensor self calibrates to show 400ppm as outdoor / minimal concentration. I was very upset to find out that it's not correct. In the last 5 years outdoor

My CO2 sensor self calibrates to show 400ppm as outdoor / minimal concentration. I was very upset to find out that it's not correct. In the last 5 years outdoor concentration rose from ~400 to ~420. Guess my kids won't be able to maintain < 500ppm.