The paper presents the analysis of scale functions of free energy in physical variables, their structure being specified and an asymmetric scale equation of state being derived. A method to define scale function parameters in physical variables has been developed. It is based on comparison of appropriate components of free energy and its partial derivatives in physical variables and parametrically on the critical isochore and critical isotherm. In compliance with the requirements of recent theory of critical phenomena the asymmetric scale equation of state in density-temperature variables proposed in the paper reproduces equilibrium properties of a real system –liquid-vapor – widely about the critical point.