The testo 416 also has a hold mode that allows you to save the most recent reading as well as min/max values. The average air volume will next be calculated using the timed and point mean value calculations. Simply enter the duct cross section area into the air flow meter to calculate the air volume. The air flow meter is suitable for measuring air flow and air volume in air ducts because it features a permanently connected telescopic sensor that can be extended to a maximum length of 890 mm and a small vane with a diameter of 16 mm. On an easy-to-read, backlit display, the testo 416 air flow meter gives quick and accurate air flow readings.