Steam Vlookup Interpolation Example
This Excel spreadsheet uses the Vlookup command on a table of data, and interpolates for data when your entering value is between entering values of your data table.
You can copy and modify this spreadsheet for your own purposes.
This is meant as an Excel tool. If you are really going to use it for Steam Properties, go to the NIST website and fill up the data table with many more rows of data.