A simple device for the demonstration of Bernoulli’s Law. Similar devices fine extensive application in everything from carburetors of IC engines to aircraft airspeed indicators. Comprising of a horizontal glass tube having three cross sections along its lengthwise, narrow and wide respectively, with wide cross-sections having same size. One short, side tube projects from each of the three cross-sections for connecting to the manometric tubes. Also included is a three egged manometer tube joined to a common horizontal tube. When gas is flowing through the venturi tube with manometer filled with colored water, the relative pressure at the three points of the tube is evident from the water level in manometers.