The air in every indoor environment is different, and the Indoor Air Quality Monitor on this device needs some time to calibrate to each new space. Levels of humidity, aerosols and other TVOCs (Total Volatile Organic Compounds), can vary significantly from home to home or building to building. As such, this device requires a calibration period that takes approximately 4 days to complete before you can expect accurate indoor air quality readings.
The calibration process happens automatically upon setting the device, you don't have to do a thing. It's important to note, however, that smoke and/or indoor carbon monoxide detection from this alarm will begin working immediately upon setup.