A unit for measurement of the velocity of air flowing into or out of an opening such as the heating or air conditioning register or grill. An open end of a collecting section is placed over the opening and the air flows through a measuring section at the opposite end of the chamber. The measuring section includes a pair of hollow manifold tubes each having a smaller diameter, hollow sensing tube mounted coaxially therein. Air flows into a plurality of probes communicating with the interior of one manifold tube, into the associated sensing tube, through a velocity meter, through the other sensing tube into the other manifold tube, and out through a second plurality of probes also positioned at the opposite end of the collecting section. An orifice or constriction in the line leading to the flow meter inlet controls the flow and allows for full scale deflection of the meter within a selected range to permit accurate calibration.
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