A multiple opening panel press is described with a plurality of movable platens which are individually controlled to adjust the spacing between adjacent platens to a predetermined panel width. Position-sensor transducers are employed to produce control signals corresponding to the platen positions which operate control cylinders by associated valves to adjust the platen spacing. The transducers are preferably sonic waveguides which interact with permanent magnets fixed to the movable platens to generate platen position signals which are applied to an automatic control system which includes a computer that produces the control signals.