Developed by Russian National Committee (RNC) of
International Association for the Properties of Water and Steam (IAPWS).
This calculation page is based on the
"Supplementary Release on Backward Equations for Pressure as a Function of Enthalpy and Entropy p(h,s) to the
IAPWS Industrial Formulation 1997 for the Thermodynamic Properties of Water and Steam" 
provided by IAPWS.
Detailed information about used equations, constants, range of validity etc is presented in PDF version of IAPWS
document which can be downloaded from IAPWS web site www.iapws.org