In their defense, they usually mention this requirement in the manual.

Sure but do you take your CO2 meter for a walk?

When nobody is home so there's no CO2 being emitted, it goes down to outdoor levels within a couple of hours if your windows are open even a crack.

If you have a meter that shows you a graph on your phone, you can watch it reach equilibrium. It's very obvious.

Etheryte 3 days ago | parent | prev [-]

And in similar vein, when was the last time you read the manual for a household appliance?

	▲	imp0cat a day ago \| parent [-]
		Both fair points. I like to familiarize myself with any appliance I buy, so I tend to read the manual at least once. And yes, it's usually a waste of time. :)