I made an Android App to calculate the CS ratio and FDR on the phone. No internet connection required.
On the bottom of the screen you can choose between 2 and 3 belt setup. Type in the number of teeth of your pulleys, the spur and pinion into the text-boxes and hit calculate. The calculator will store your setup, so that you don´t have to type everything again next time you only want to change one pulley.
I hope it will be up on cnet for download soon. In the meantime you can download it here >>>
So far I only tested it on my own phone and an emulator, if you have any issues with the app, please send me a PM. - Enjoy.