Those readings should be taken in an equal area or Log-T method per NEBB procedural standards. Not just at the center point of the duct. 2,6,9 inches on the vertical readings. The flow velocity tends to be lower near the duct walls due to friction. Yes, the average will be close when the velocity is tallied up. However, traverse points according to the National Environmental Balancing Buerou need to be one of the two methods.
