A psychrometer is used to measure the dry bulb temperature along with the humidity of air. A majority of in-duct psychrometers are meant to have a constant airflow across them and this tool does that. For example, if there is a need to measure the temperature/humidity at different places in an open room, this tool would allow for that because it is designed to produce a constant airflow over the sensor of the psychrometer. It does this with a fan that attaches to the end cap that goes over the open end of the air tunnel and this fan is located 2.5 duct diameters away from the sensor so that the airflow is constant within the space being measured. Another way to help avoid turbulent air in the air tunnel is by the air straightener that attaches to the other end of the air tunnel. The reason that it attaches to the other end of the air tunnel is because it is a pull air tunnel where the fan draws the air through the air tunnel to exit through the fan.