The influence and importance of the relative static permittivity (RSP) in electrolyte equations state is examined for case aqueous sodium chloride. Using SAFT-VR Mie model, Debye-Hückel (DH) or Mean-Spherical Approximation (MSA) terms, as well Born-solvation term, are used to formulate an equation state. RSP obtained from a variety models, each differing their dependencies; we consider constant...