783,872. Calculating apparatus. BURROUGHS CORPORATION. Jan. 5, 1955, No. 326/55. Class 106 (1). In a machine having a second totalizer engaged with and in opposite sense to a first totalizer, so that the accumulations in the two totalizers are always complementary and the second totalizer yields a true negative total when the first is overdrawn, selection of the appropriate totalizer for total-taking is determined by mechanism controlled by the highest order pinion of at least one of the totalizers in accordance with changes in sign of the accumulated total. The invention is applied to the machine described in Specifications 741,583, 741,586, 766,127, 783,869 and 783,871, which comprises differential bars 31 connected to pairs of racks 75 having upper adding and lower subtracting rack sections engageable with the wheels of two totalizers. In the present machine, items are accumulated in both totalizers, the lower totalizer being engaged normally, i.e. with the upper rack sections 76 for positive items and the lower rack sections 77 for negative items, whilst the upper totalizer is engaged oppositely and so registers the complement of the amount registered by the lower totalizer. When, therefore, the lower totalizer is overdrawn, the true negative total can be obtained from the upper totalizer. The present invention provides means which automatically select the upper totalizer in place of the lower totalizer for total and sub-total taking when the lower totalizer is overdrawn. In total taking, the other or overdrawn totalizer is engaged with its upper adding racks during the second half cycle in order to clear the complementary value registered. Totalizer engagement.-As fully described in Specification 741,583, totalizer engagement is effected by rearward movement of a link 116, Fig. 12, a slot in the link normally engagnig a lower stud 52 on a disc 50 and so rotating the disc counterclockwise to engage the lower totalizer with its upper add racks 76 and the upper totalizer with its lower subtract racks 77. When negative items are being entered, the link 116 is raised to engage an upper stud 52 on the disc 50 which is then rotated clockwise to engage the two totalizers with their respective other racks. The connections between the disc 50 and totalizer frames are yielding, so that totalizer engagement can be additionally controlled directly as later described. Cyclic operation of the machine is effected by forward and return reciprocation of an operating member OP. In total and sub-total operations, however, spring means described in Specification 741,586 restore the transfer mechanism immediately upon depression of the total or sub-total key, in order that the operation can be accomplished in a single cycle. Totalizer selection in total and sub-total operations.-As long as the lower totalizer carries a positive amount, the link 116 maintains its normal engagement with the lower stud 52 of the disc 50, Fig. 12, so that the lower totalizer is engaged with its upper add racks to control differential adjustment of the bars 31 in total taking. When an overdraft occurs in the lower totalizer, a selector shaft 136 moves clockwise to remove a pin 165 out of blocking engagement with a stud 169 on a lever 166. A cyclic resetting lever 111 is then able, through a spring 172, to rock the lever 166 clockwise, provided a stop arm 173 has been moved clear by depression of the total or sub-total key, and the lever 166, through a link 167, raises the link 116 to cause the upper totalizer to engage its upper add racks in place of the lower totalizer. In either event, the other totalizer is prevented from engaging its negative racks by means of a pivoted blocking member 195, Fig. 13. This member is adapted to be actuated by engagement of a stud 200 with a hook 199 pivoted to the member, the stud being carried by an arm 101 secured to a cyclically operated resetting shaft 100. The hook 199 rests on a stud 193 on a link 180 supported by a lever 184 normally held raised by the cyclic operating member OP. The lever 184 is released to a spring 218 immediately the operating member OP moves forward at the commencement of a cycle of operation, and this lowers the link 180 and stud 193. In item entering operations, this occurs before the arm 101 moves and the hook 199 is therefore, moved clear of and not actuated by the stud 200 on the arm 101. In total and subtotal operations, however, the shaft. 100 and arm 101 are rocked clockwise by the spring means, referred to above, immediately the total or sub-total key is depressed; the stud 200 consequently moves the hook 194 rearwardly and rocks the blocking member 195 to engage blocking surfaces thereon under studs 45 and 48 secured to the frames of the two totalizers, so preventing either totalizer from engaging its negative rack 77. Overdraft responsive mechanism.-Tens transfer is effected by the pivoting of zero abutment rockers 82, Fig. 1, to permit an additional step of return movement of the differential racks 75. Additional such rockers 82, Fig. 9, are provided above the highest orders and are tripped by passage of the highest totalizer wheels from " 9 " to " 0 " or vice versa.. Extensions 144, 146 of these rockers are adapted to actuate arms 140, 141. on the selector shaft 136 so that the selector shaft is rocked clockwise, Fig. 12, to release the pin 165 from the stud 169 and reverse the totalizer engagement, as above described, when an overdraft develops in the lower totalizer. The shaft 136 is restored when the upper totalizer becomes overdrawn as the lower totalizer reverts to the positive condition. A pivoted, latch 151 is adapted to block one or other of the additional rockers 82 to prevent its actuation by the passage of the related totalizer through zero positively. Normally, for positive items, this latch 151 blocks the lower rocker but is moved to block the upper rocker and release the lower, when negative items are being accumulated. Total-taking.-In total-taking operations it is necessary to engage the overdrawn totalizer with its positive rack at the end of the first halfcycle in order to clear it during the second halfcycle. This is accomplished by means of a lifter link 250, Fig. 21, which is swung by operation of the total key to engage an ear 255 or 256 under the frame stud 45 or 48 of the overdrawntotalizer, and is then raised by the cyclic operating member to engage the overdrawn totalizer. Depression of the total key displaces a link 229, Fig. 18, rearwardly, the link having been positioned by the selector shaft 136 so that a notched plate 234 on the link engages the appropriate one of two studs 238 on a block secured to a shaft 240. This rocks the shaft in one direction or the other and correspondingly swings the link 250, Fig. 21, through a link 248. The link 250 is now positioned to be raised by a stud 259 on a link 257 pivoted at 260 to a multi-part lever 269 pivoted at 100. At the end of its forward stroke, the operating member OP engages a cam edge 271 of the multi-part lever so raising it and the link 250 to engage the overdrawn totalizer with its positive rack. A latch engages over a stud 274 on the multi-part lever to maintain the register engaged throughout the rearward movement of the operating member, the latch being tripped at the commencement of the next operating cycle.