I made a little Excel spreadsheet to convert the values of FRNs > .999 > 90% Face > 40% > 35% Face.
It will convert any value to any other value. Here is the NEW screenshot:
Just type in the current spot silver price and your known value into the correct white cells and the other 5 values will automatically calculate for you.
Download this file to use it:
http://www.idahocopper.com/Converter.xls