I should add: it was rather fancy as it could display graphs and such. But in the end that not very useful, after a few days of watching the readings you start

I should add: it was rather fancy as it could display graphs and such. But in the end that not very useful, after a few days of watching the readings you start to understand when CO2 increases (people) and decreases (ventilation). It never reached unhealthy levels of CO2 in our home.