Developed by Russian National Committee (RNC) of
International Association for the Properties of Water and Steam (IAPWS).
This calculation page is based on the
"Revised Release on the IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use" 
provided by IAPWS.
Detailed information about used equations, constants, range of validity etc is presented in PDF version of IAPWS Release which can be downloaded from IAPWS web site www.iapws.org