The aim of the thermodynamic consistency test is the examination of correspondence between the basic thermodynamic equations and a given calculation of measured data. In this test we have to face the problem of choosing an approximating function that causes negligible error with respect to the errors of measured data. We discuss the different solutions of Vapour Liquid Equilibrium and Speed of Sound data testing focused on numerical mathematics and information technology. We present - as Internet downloadable files: results of general formal algebraic calculations, software and thermodynamic examples - the application of our newly developed numeric approximation method, minimal energy Bezier surfaces over triangles and rectangles. The approximated surfaces are depicted by an own developed PASCAL graphic software that can be downloaded, as well.