The AAV3 is an anemometer accessory head for use with our modular instruments that measures air velocity and temperature in English or Metric units: -Feet/Min M/s MPH KM/hr. Degree F (Degree Fahrenheit) or Degree C (Degree Celsius). Multiply your air velocity by the register s free area to estimate CFM or diagnose duct blockages and quickly check the airflow balance in a conditioned space. Use with our DL3 Data Logger to track airflow or temperature over time. Features average and real time testing modes.