TSI’s IAQ-CALC Meters are outstanding instruments for investigating and monitoring indoor air quality (IAQ). The Model 7515 is a cost-effective meter for carbon dioxide (CO2) measurements. The Model 7535 adds data logging of CO2. The Models 7525 and 7545 simultaneously measure and data log multiple parameters. The Model 7525 measures CO2, temperature, humidity, and calculates dew point, wet bulb temperature, and % outside air. The Model 7545 adds carbon monoxide (CO).