Viscoelastic fluids are currently used for a wide variety of applications in food, chemical, cosmetics and pharmaceutical industries. They are dilute or semi-dilute solutions of high-molecular-weight polymers. For some concentrations, the controlled stretching of the fluid leads to the formation of beads-on-string structures which are characterized by drops connected by a filament. In our case, the controlled extension of the viscoelastic fluid is achieved thanks to an in-house filament stretching device. In order to analyse the 3D dynamic of the beads-on-string structure, i.e. to measure the displacement and the velocity of the bead-like drops during and after the stretching process, we use double exposure Holographic imaging. Holography allows us to choose a 3D volume of space to capture the entire phenomenon. Thanks to Holography, we can focus on one or several planes along the optical axis in order to estimate the 2D coordinates of beads in each plane. The computation of these planes leads to a reconstructed volume where the 3D displacements of beads along the x, y and z axes can be extracted. The dynamic of beads-on-string structures may depend on several factors which are linked to the fluid properties but also to the initial state and elongation parameters. The aim of this work is to experimentally identify the factors which are appropriate to observe a repeatable beads-on-string structure before studying the influence of an orthogonal air current.