The Rayleigh Ohnesorge jetting extensional rheometer (ROJER) enables measurement of very short relaxation times of low viscosity complex fluids such as those encountered in ink-jet printing and spraying applications. This paper focuses on the design and operation of the ROJER. The performance of two nozzle designs is compared using Newtonian fluids alongside a study using computational fluid dynamics. Subsequently, a disposable nozzle is developed that overcomes issues of blockage and cleaning. The operability of this design is subject to a focused study where low viscosity polymer solutions are characterized. The test fluid materials are ethyl hydroxy-ethyl cellulose and polyethylene oxide mixed with water/glycerol solutions. Results obtained by the disposable nozzle are encouraging, paving the way for a more cost-efficient and robust ROJER setup. (C) 2017 The Society of Rheology.