Measuring the unevenness of a pavement surface. As the screen member becomes blocked, it moves from a first or initial position to a second or actuated position which causes a pressure change detectable at the surface of the wellbore. The bottom core surface may be recessed beneath, coplanar with, or protruding from the bottom surface of the device. A stem attached to the forward end of the piston extends rearwardly from the forward end and away from the roller into a cylindrically enclosed body portion of the chuck.