of calender roll or 34 slice 34 is about six inches wide however depending upon the particular situation each slice may be wider or narrower additional nozzles 49 are located near the ends of the plenum 5 to compensate for the increased cooling tendency of the calender roll ends as shown in fig1 a computerized valve control device 50 controls the heating of each section of the calender roll 11 to maintain a uniform thickness of calendered material 29 a web thickness sensor 51 senses the thickness of the calendered material 29 at various locations along its width and sends signals which correspond to the thicknesses of the material to the control device 50 depending on the degree of deviation of the calendered material 29 from the desired thickness the valve control device 50 selectively directs air pressure against certain diaphragms 21 which in turn adjust the associated valves 13 so that the valves discharge a greater or lesser amount of steam from each nozzle 9 if the sensor 51 detects a thick section of calendered material 29 the control device 50 adjusts the valve 13 adjacent to that section of the calender roll 11 and allows more steam to heat that section of the roll 11 the additional steam heating the section of the calender roll 11 causes it to expand the expanding section of the calendar roll 11 decreases the corresponding section of nip 25 thus decreasing the thickness of the calendered material 29 produced by the heated section of the roll 11 alternatively when the sensor 51 detects a thin section of calendered material.