The minimisation technique proposed by Binding (J. Non-Newtonian Fluid Mech., 27 (1988) 173) was used in our Generalised Engineering Bernoulli Equation framework to relate the entry pressure and stress power. We arrived at a final result similar to Binding＇s using assumed kinematics. Through subsequent assumptions to the kinematics we finally arrive al a result exactly equivalent to Cogswell＇s technique (Trans. Sec. Rheol., 16 (1972) 383). Thus, these two techniques are related in this general framework. The techniques were used to predict elongation flow properties of a polymer melt and polymer solution. The results for the polymer melt clearly show Cogswell＇s technique is adequate at high elongation rates. All these techniques require minimisation of the stress power with respect to the how volume and discussion is given as to the validity of this minimisation technique. In addition, the approximate variational technique we propose gives clears limits as to when a technique, such as Cogswell＇s, can be applied.