Freesteam implements the international-standard steam tables from the International Association for the Properties of Water and Steam, IAPWS. The correlations for both IAPWS-IF97 and IAPWS-95 are provided, although the emphasis is on the use of the IAPWS-IF97 correlation.
To get to the meaty bits, see the SteamCalculator, Solver2 and Solver classes, and after that have a look at SatCurve, B23Curve, B13Curve and Boundaries.
Where possible, C++ references have been used, and methods have been suitably 'constified', but there may still be gaps in that.
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.