It’s a good benchmark: it errs on the side of caution. If the carbon dioxide level outside is low enough, and it probably is, then the carbon dioxide the meter measures has probably come from someone else in a public space. COVID does not hang in the air forever like carbon dioxide does. Not all carbon dioxide has come from a person. So, a cheap, mass-produced device can give a figure that in the worst case - all carbon dioxide has come straight from another person - may be proportional to COVID risk.
This is also people thinking about science. Let’s all be really, really quiet, everyone. Don’t tell them off because they haven’t done it your way first go. Maybe they will go on doing it. Maybe the healing has begun…
