Caskey 3 Barlage (1971) used a vertical oscillating jet and directly measured the wavelength characteristics with a Gaertner two-coordinate cathetometer . Instead of the usual drawn glass tubing for the orifice, they constructed the orifice from 2 .0 mil Mylar film coated on both sides with paraffin. The Mylar film was attached to a Parker tubing nut to form the diaphragm orifice .