A method for making fluid elasticity measurements using an extensional viscometer (100) is disclosed, where stress is not directly measured but is inferred from an accurate measurement of the change in the rate of flow of a liquid during passage through a vertical capillary (104). The flow rate changes when the liquid jet, also called the liquid filament, leaving a first capillary (104), is stretched by the application of vacuum forces. Steady flow is established almost instantly by using a constant liquid head (102, 118) above the capillary, and the flow rate is determined by timing the interval for liquid to drain between two marks (110, 112) on the liquid reservoir surface. Extensional viscosity can be calculated as a ratio of the tensile stress and stretch rate of the liquid at different axial positions.