Abstract: A platen press has upper and lower platens each provided with at least one rigidifying beam. A group of hydraulic cylinders spaced about over one of the platens serves to urge the two platens together in a pressing direction to compress a workpiece--plywood, fiber mat, chipboard, or the like--between the platens. During pressing the platens and their rigidifying beams bend somewhat. This bending is measured by an apparatus which comprises a flexible strand, holders at the ends of the one beam for gripping the ends of the strand and holding same straight and under tension, and sensors fixed on the one beam at a location between the ends of the one beam for measuring the displacement of the strand relative to the beam at the location during pressing. This sensor lies wholly out of physical contact with the strand.