Exec's 4" (10cm) Large Vane Thermo-Anemometer series allows for more precise readings on larger size ducts. Each meter simultaneously displays Airflow or Air Velocity and Temperature. This model also measures Relative Humidity, Wet Bulb and Dew Point. This product is NIST Certified which indicates that the product is traceable to standards provided by the National Institute of Standards and Technology (NIST).