Extech 407119-NIST - NIST Calibration Certificate - CFM Hot Wire Anemometer Heavy Duty features: Accurately measures Air Flow (CFM/CMM) or Air velocity plus °F/°C Temperature; Air velocity measurements as low as 40ft/min; Telescoping probe is ideal for use in ducts and ventilating systems; extends up to 4ft (1.22m) long; Built-in RS-232 PC Interface, etc.