The aim of thermodynamic consistency tests is the examination of correspondence between the basic thermodynamic equations and a given set of measured data. These equations contain derivatives of thermodynamic functions, so we can not avoid numerical approximations: a principal problem is to choose an approximating function that causes negligable error with respect to the possible systematic error of the measured data. For evaluation of the function values and for the estimation of model parameters and statistical testing we usually have to apply more than one software. We discuss the different solutions of Vapour Liquid Equilibrium and Speed of Sound data testing with respect to numerical mathematics and information technology.