TSI Velocity matrix probe with telescopic handle, two 8 feet neoprene tubes. Velocity matrix used to measure face velocities of HEPA filters, chemical fume hoods, laminar flow benches, filter banks, kitchen exhausts and other applications where a large surface area needs to be measured. The 16 point grid covers one square foot area and averages the air velocity while minimizing the affects of turbulence to produce a stable reading.