9102. Wade, H., [Burroughs Adding Machine Co.]. April 17. Adding and subtracting apparatus with operating-means; printing totals and sub-totals. -Adding and listing machines, in which the movements of the type-carriers to set-up and print a total are determined by the numeraldrums of the registering-mechanism, are provided with (a) means for displaying and printing a negative total, i.e. a total of amounts overdrawn, and adding unity to such total, or subtracting a unit therefrom when a change from addition to subtraction or vice versa occurs; (b) an interlocking arrangement for the total key and operating-lever to ensure the correct working of the apparatus. The invention is shown as applied to machines of the Burroughs' type as set forth, for example, in Specifications 17,126/93 and 21,268/97. The registering- mechanism comprises a single series of numeraldrums 916<a>, Fig. 4, bearing two sets of complementary numbers relatively displaced so that complementary pairs of digits register with apertures 91, 92 of a shield 90. Attached to the numeral-drums are the usual pinions 916 of the Burroughs' machines, permanently engaging with pinions 916<c>, Fig. 2, the numeral-drums and both sets of pinions 916, 916<c> being mounted in a rocking frame or cradle 9L, Fig. 6, pivoted to the usual main rocking frame 910L, which is supported by the cross-bar 900. If the controlling-lever 10 is pulled forwards to change the operation from addition to subtraction, the lower end 10<f> of the lever rocks the arm D causing the locking-arm G to disengage the arm 9<e> of the cradle 9L, whereupon the cradle will be rocked by the forked arm H, which is in turn lifted by the co-operation of a roller h<2> with a cam-slot 10<c>. The. lower pinions 916<c> will thus, at the next movement of the main frame 910L due to the usual pitman 914, be adapted to engage with the racks 610 and the rotation of the numeral-drums 916<a> will be reversed. A change in the position of the controlling-lever 10 with the accompanying rocking of the cradle 9L, 9R, Figs. 6 and 8, is adapted to cause the addition of an extra unit if the operation changes from addition to subtraction. and the deduction of the unit in the case of a change from subtraction to addition. In a change of function from subtraction to addition, when the upper pinions 916 are to be normally engaged with the actuating-racks on their upward stroke, the rocking of the cradle to the position shown in Fig. 8, brings a projection a<1> on a pivoted tappet-piece A, frictionally mounted on the main accumulator-frame 910R, opposite the upper foot a of a lever 413<c>, resembling the usual transfer levers of a Burroughs' machine, but co-operating with the actuating-rack 610 of the units' denomination. The rocking of the frame 910R to bring the upper pinions 916 into engagement with the racks causes the projection a' to engage the foot a and rock the lever 413<c> so as to release the pin 610<c> and allow the rack to undergo the usual additional movement. A latch 411 resembling the usual latches for the transfer levers of Burroughs' machines engages the lever 413<c>, when tripped by the tappet-pieec, to allow the additional movement to take place. The projection b<1> on the tappet-piece A similarly co-operates with the lower foot b of the transfer lever on the first operation of the machine after a change of function from addition to subtraction. To prevent an addition or subtraction of a unit at every subsequent operation after a change in the nature of the operation, a lever C', Fig. 8, pivoted at c is actuated by a pin c<1> on the usual full-stroke sector 311, and at the first operation after a change in the function of the machine and immediately after the rocking of the lever 413<c> by the tappet-piece A, one of the projections c<4>, c<5> coacts with one of the corresponding pins a<2>, b<2> on the projections a', b<1>, respectively, and rocks the tappetpiece so that it is engaged by the front or rear notch of a latch F and retained in an inactive position just clear of the lever 413<c>. Fig. 16 shows an example of the work performed by the machine. Transfer mechanism.-Cams 920, 921 associated with the two sets of pinions 916, 916<c>, Fig. 2, co-operate as usual with feet 413<a>, 413<c>, respectively, on the transfer levers 413. Interlocking.-After a change has been made in the nature of the operation, two blank strokes will usually be necessary before a total can be printed, one to restore the actuating-racks which have undergone an additional movement at transfer and to add or subtract the required unit, the second to restore the units actuating- rack. The actuation of the controlling-lever 10 rocks a lever D, Fig. 6, and moves rearward the bail 424R, 424L, if this is not already in its rearward position owing to the movement of the transfer latches 411. A gravity catch E, Fig. 8, thereupon engages the bail and reengages it after temporary release bv the camedge c' of the lever C C<1> when rocked by the pin c<1> described above, if any transfer levers or latches are still unrestored. A second blank stroke restores the units' rack and permits the bail 424R, 424L to move forwards, thereby allowing the depression of the total &c. key. Specification 442/12 is also referred to.