The Fan Assessment Numeration System (FANS) is a measurement device for generating ventilation fan performance curves. Three different-sized FANS currently exist for assessing ventilation fans commonly used in poultry and livestock housing systems. All FANS consist of an array of anemometers inside an aluminum shroud that traverse the inlet or outlet of a ventilation fan. The FANS design has been updated several times since its inception and is currently in its fourth-generation (G4). The current design iteration (FANS-G4) is reported in this article with an emphasis on the hardware and software control, data acquisition systems, and operational reliability. Six FANS-G4 units were fabricated at the University of Kentucky (UK) Agricultural Machinery Research Laboratory and calibrated at the University of Illinois Urbana-Champaign (UIUC) Bioenvironmental and Structural Systems (BESS) Laboratory. Results demonstrated that the FANS-G4 was capable of measuring volumetric airflow to within 0.6% of full-scale (FS), which ranged from 15,000 to 56,000 m3 h-1.