[stanislavb]

I use the same CO2 meter as the author has showcased. It's amongst the most accurate ones on the market at the moment (home grade). It uses a The Non-dispersive infrared sensor (NDIR) which is much more accurate than most sensors on devices sold online for $100-200. In fact, it actually measures instead of "estimates" the level of CO2 (as most cheap ones do).

[amitamit]

Agreed!! I have also tried many different CO2 meters (all consumer-grade) and Aranet has been consistently the most accurate among the CO2 meters I have used.

[CoastalCoder]

How did you determine the accuracy of your CO2 meters?

[amitamit]

I measured the CO2 levels in one room using several different CO2 monitors - under similar conditions (steady-state with one person in the room, windows partially open) on different days; Aranet readings were the most stable and consistent, while matching the "expected ppm".

I also tested the monitors by exhaling directly on them, and confirming the change in readings.