Fast Follow Counting


I have an idea. For it to work I need to know the # of fast followers I have. I am not trying to get the phone number or any personal data. I just need to be able to measure the follow / stop rate. Is it possible to develop something that can do this (if it already isnt out). I have been searing the net / board since sunday and I see nothing about such a thing. Is it doable?

It would be nice to know average length of follow too but what I posted above is the most important