The VOLU-probe/FI Fan Inlet Airflow Probe consists of a pair of offset mounted traverse probes that are installed directly in the fan’s inlet bell mouth at the throat. The VOLU-probe combines the air processing effect of the nozzle-shaped fan inlet with the multi-point, self-averaging Pitot tubes to accurately measure inlet velocity pressure and calculable air volume with an accuracy of ±3% for most fan types. Available in both aluminum and stainless steel. Patent No. 3,733,900.