The Extech 407119 Heavy Duty CFM Hot Wire Thermo--Anemometer uses a telescoping probe (extends up to 3 ft) which is ideal for use in ducts and ventilating systems. It can accurately measure Air Flow (CFM/CMM), Air Velocity and Temperature. Air Flow can be displayed as an instantaneous value or up to a 20-point average. Additional functions include Data Hold, Min/Max, and Auto power off. A built-in RS-232 interface can be used with optional Data Acquisition software and cable for recording measurements directly to your PC.