Plug the static pressure probe into the "low" port of the differential pressure sensor.
Plug the total pressure probe into the "high" port of the differential pressure sensor.
Position the total pressure probe so it points along the duct's air flow.
Stand the static pressure probe perpendicular to the duct's air flow.
Note the air flow's velocity pressure from the differential pressure sensor's display.
Find the square root of this answer. If the velocity pressure is 0.75
0.75 ^ 0.5
Multiply your answer by 4,005 to convert it to feet per minute.
0.866 * 4,005
Measure the length of the duct in feet.
Measure the width of the duct in feet.
Multiply the length by the width. If the length and width are 2 and 2.5 feet respectively:
2 * 2.5
= 5 square feet
Multiply the answer by the answer to step 7.
3,468 * 5
= 17,340 cubic feet per minute.