1. A method of leak testing masks comprising the steps of arranging a flowmeter so that a pair of manifolds are on opposite sides of a central screen, a pair of air-controlling orifices are located in contact with said manifolds anD on the side thereof opposing said central screen, a pair of screens are located in contact with said air-controlling orifices and on the side thereof opposing said manifolds, a pair of retaining members are located in contact with said pair of screens and on the side thereof opposing said air-controlling orifices, and means are provided for connecting said flowmeter to a recording device; hermetically sealing said flowmeter at the mouth area of the mask to be tested; connecting the recording device connection means of said flowmeter to a recording device; installing said mask on a person''s face; exhaling and inhaling into the mask to produce a pressure drop across the pair of screens; producing a pressure drop to alter a differential pressure developed across the central screen to produce a linear pressure signal related to an instantaneous air flow; and monitoring any leakage due to external pressure as a difference between the linear pressure signal and the pressure on inhaling while said person inhales and exhales.