Article Spinning - Does this Exist?

I am using TBS to spin some content and as I go I can see the percentage indicator at the top telling me how unique it is compared to the original copy, but the fact that you are changing the original copy as you spin means that its not good for testing one copy against another.

This is fine but what I want is somewhere that I can paste an original copy in one box and then the spun copy in another and click "compare" and it tells me how unique the spun copy is.

Does this is exist?