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Claim 1

APPARATUS FOR MEASURING SURFACE IMPERFECTIONS IN STRANDS OR SHEETS OF PLASTIC MATERIAL, COMPRISING A SIGNAL PICKUP ASSEMBLY, DRIVING MEANS FOR DRAWING SAID MATERIAL PAST SAID PICKUP ASSEMBLY, VIBRATION DAMPING MEANS, SAID DAMPING MEANS BEING DISPOSED IN PHYSICAL CONTACT WITHE SAID MATERIAL AND DISPOSED ON THE SIDE OF SAID PICKUP ASSEMPLY WHICH IS REMOTE FROM SAID DRIVING MEANS, SAID PICKUP ASSEMBLY INCLUDING A HOLLOW COIL HAVING A SIGNAL WINDING, A ROD-LIKE STYLUS MEMBER ADAPTED TO BE IN SUBSTANTIALLY CONTINUOUS CONTACT WITH THE SURFACE OF THE MATERIAL BEING MOUNTED TO PERMIT FREE LONGITUDINAL VERTICAL MOVEMENT THEREOF, AND HAVING A PORTION WHICH EXTENDS INTO THE INTERIOR OF SAID COIL, MAGNETIC MEANS SECURED TO THAT PORTION OF SAID STYLUS WHICH EXTENDS INTO SAID COIL, WHEREBY LONGITUDINAL MOTION OF SAID STYLUS MEMBER MOVES SAID MAGNETIC MEMBER WITH RESPECT TO SAID SIGNAL COIL AND INDUCES AN ELECTRICAL SIGNAL THEREIN, INDICATOR MEANS FOR REGISTERING SAID SURFACE IMPERFECTIONS, AND ELECTRONIC AMPLIFIER MEANS HAVING AN INPUT CIRCUIT COUPLED TO SAID SIGNAL COIL AND AN OUTPUT CIRCUIT COUPLED TO SAID INDICATOR MEANS.