static pressure is express in injure of water. you might here in the fan generate to injure of negative static pressure which me to the pressure inside the duct on the suction side on the fan. it's 2 injure of water less than the pressure outside the duct. the pressure in cloud ventilation application are relatively small. the use of conventional
measurement suggest injure some mercury or pound per square inch.
what we often pressure express and very small member.