Uniform downflow velocity for A1 cabinets should be taken as per NSF/ANSI 49: a. 6.0 inches below the diffuser b. at multiple points across the workspace, using equal points in the horizontal plane 4.0 inches above the bottom edge of the window frame. c. along the centerline of the work surface at a height of 4.0 inches above the top of the access opening. d. At multiple points across the work access opening on a grid as specified on the data plate. e. with no less than 2 readings per 1 foot.