Testo 417 Vane Probe CFM Anemometer with built-in 4 in. vane, incl. temperature measurement, battery, softcase and calibration certificate. The high quality bearings in the testo 417 handheld anemometer yield nearly Friction-free rotation for direct measurement of air velocity with an NTC sensor used to determine air tempeature. The vanes cover all the measured area - no airflow is lost between the vane and outer ring. The 4" head averages true flow over its entire area, not just responding to local stray eddies. Just input the duct cross-sectional area (from 0.2 sq. in. to over 100 sq. ft.) to see accurate, real-time CFM calculations. Simply toggle betweem velocity, CFM, and temperature readings on the clear, backlit display. Flow direction is indicated by an arrow in the display. Timed or multi-point averages are easlily accomplished with all parameters and caluclations. Mn-Max values can also be displayed. The "Hold" function frezes current readings in the display making data recording easy.