R Square of Resistive Cloth

I am looking for a way to test the "r Square" of a resistive cloth. I would like to do this while it is still on the web, We currently cut squares out of the cloth and test them on a seperate fixture. But when we do this we lose material at the point we cut the sample out. has anyone ever seen any type of a test instrument that can isolate a square while on a large roll and get an accurate (ohms per square) reading? Or do you know of other processes to achieve a test for this?

Thanks for any help or advice.