789,385. Recording-apparatus. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Feb. 27, 1956 [March 10, 1955], No. 7126/55. Class 106 (4). A potentiometric recorder with a. linearly movable shaft 14 comprises y pens spaced apart along the direction of movement of the chart and capable of moving together in the direction transverse to the movement of the chart, means for moving the pens to x transverse stations with zero signal input so that xy areas are available on the chart to record quantities measured at xy points by selection of the appropriate pen and the appropriate station. Apparatus for recording the voltage across each of 48 pairs of terminals 155, Fig. 8, successively in repeated cycles over 24 hours comprises a three-bank uniselector switch whose wiper arms 138, 139, 140 are stepped on from contact to contact at 30 sec. intervals, successively sampling each voltage by connecting one terminal 156 of each pair to a bridge circuit through the wiper 140, while the wiper 139 selects each pen P1 to P8 in turn for six successive samplings and the wiper 138 adds in resistances 142 one by one in cycles of six to shift along the potentiometer wire 51 the zero position of the wiper 52 with which moves a sliding bridge structure 15, Fig. 7, carrying an arm 16 holding eight spaced electrode " pens." During the last second of each 30 sec. interval an electromagnet 108 causes all the pens to rock into contact with the chart 14, followed by the operation of a change-over switch 145 to discharge a condenser 146 through the selected pen to record the value of the voltage indicated .by the position to which the wiper 52 has been - moved by servomotor mechanism 159 to achieve balance of the bridge circuit. Chart driving mechanism. The chart 14 is driven from an upper drum frictionally held on a shaft 65, Fig. 3, driven at constant speed against the torque introduced by a band brake 69, which torque is greater than that given by the friction between the drum and shaft, so that the chart can be advanced by hand about 14 inches at the end of every 24 hours in preparation for the next 24-hour cycle, without introducing slack into the drive to the shaft 65. The chart is held in tension by a spring 81, Fig. 3a, interconnecting a shaft 78 and a knob 80 which is turned to tension the spring and advance the chart. The tension is prevented from escaping by a pawl 149 acting on gearing secured to the knob 80 and, while taking up the slack in the chart 14 as rotation of the drive shaft 65 releases it from the upper drum, the spring 81 causes the strip to be taken up by a drum 82 secured to the shaft 78. Electrode " pen " holder arm. Two blocks 89, 90, Fig. 5, fixed to a channel section member 91 house a push rod 92 operated by a lever, pivoted in the lower, forked end 106, to rock eight bellcrank levers 94 to bring tungsten wire tips of electrodes 96 into contact with the chart. Electrical connection is made from the electrodes 96 through wires 99, connectors 98, cable 20, wipers and bus-bars to the contacts of bank 152 of the uniselector switch.