HCHO - formaldehyde levels, usually released by manufactured wood products (plywood, MDF, etc.), such as new furniture
Humidity - dampness in the air
Temperature
Raw data is only so useful, so it shows Normal/Moderate/Unhealthy on the screen to give you a meaningful description (and beeps if levels are dangerous).
Connects to a computer, via USB A-to-micro-B, to save logs (CSV format) for analysis. USB cable also used for charging the internal battery.