The E Instruments HO621 is a 2 x 2 ft (610 x 610 mm) measuring hood for DBM 620 air flow meter kit. It is airtight and has a transparent viewing window that allows the user to see through the vent to ensure the hood is in the proper position. The HO621 measuring hood comes with airflow straightener for swirling diffuser and is supplied with foldable frame and sheath.