A device for in-situ fan airflow measurement, known as the Fan Assessment Numeration System (FANS) device, previously developed and constructed at the USDA-ARS Southern Poultry Research Laboratory, was refined at University of Kentucky as part of a project for quantifying building emissions from mechanically ventilated poultry and livestock facilities. The FANS incorporates an array of five propeller anemometers to perform a real-time traverse of the airflow entering fans of up to 137 cm (54 in.) diameter. Details of the updated design, including hardware, software, and calibration methodology are presented. An error analysis of the flow rate, and calibration results from ten FANS units, is provided. Sufficient details of fabrication and calibration are presented so that interested readers can replicate a FANS for their use. Full design details are available at www.bae.uky.edu/IFAFS/FANS.htm.