An SER Universal Testing Platform represents a widely used instrument determined for the measurement of elongational viscosity of various materials. Apart from an initial pre-selection of materials and an a priori range of extension strain for which this method can be applied, there is a series of other factors substantially influencing quality and reproducibility of the obtained results. They are prevailingly connected with the preparation of the samples and their fixing to the elongation rheometer. Among them it is possible to name an unevenness of sample thickness, appearance of air bubbles within the material studied, slant of fixed sample with respect to the rheometer drums axes. The aim of this contribution is to show the reasons of possible bad reproducibility of elongation measurements and visually determine the ranges of selected parameters within which the measurements are acceptable.