From the developer: "Properties of Water & Steam is a software package designed for anyone who needs to have accurate properties of water. The program is based on the industrial IAPWS Industrial Formulation 1997 standard. PWS supplies you with the fastest and most stable steam functions available. The PWS Excel Add-in release combines the capabilities of MicroSoft Excel with the accuracy and speed of the PWS steam functions. PWS Excel Add-in is easy to use, automatically installs itself, and allows using different units in the same worksheet."