I am new to this field of electrical measurements and my question may sound amateurish but your suggestions will be highly appreciated. I have got a micron thick polymer sample with some kind of irregular shape. I mean with each sample the shape is being changed little bit as the shape is not in my control. I am measuring the resistance in MOhms using keithley sourcemeter with four point probe. Now my question is how to convert this resistance that I have got from Keithley sourcemeter into conductivity and resistivity.As the shape is random and irregular for my different samples,is it right for me to compare the conductivities of different sample. Your help and suggestions will be highly appreciated. Thank You.