Submitted to Rheologica Acta (2002) Filament stretching rheometer: inertia compensation revisited Peter Szabo(1), Gareth H. McKinley (2) 1) P. Szabo, Danish Polymer Centre, Department of Chemical Engineering, Technical University of Denmark, Building 423, DK-2800 Kongens Lyngby, Denmark 2) G.H. McKinley, Hatsopoulos Microfluids Laboratory, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA Abstract: The necessary inertia compensation used in the force balance for the filament stretching rheometer is derived for an arbitrary frame of reference. This enables the force balance to be used to extract correctly the extensional viscosity from measurements of the tensile force at either end of the elongating fluid column in any of the different experimental configurations that have been introduced to date. The present analysis eliminates a restriction inherent in the work of Szabo (Rheol Acta 36:277-284 (1997)).