755,413. Electronic counting-apparatus. INTERNATIONAL BUSINESS MACHINES CORPORATION. Dec. 17, 1954 [Dec. 21, 1953], No. 36570/54. Class 106 (1). In a counter having a series of stages each including a trigger circuit, input pulses are applied simultaneously to a switching circuit of each stage and each switching circuit is arranged to apply a pulse to its associated trigger only when that trigger is in a first state, the stages being interconnected so that when a trigger changes from the first state, the next trigger in the series assumes the first state. Negative input pulses are applied at t1, Fig. 1, to and gates e.g. A1, which may be double diodes and each of which has a second input connected to the left-hand anode α1 of an associated double-triode trigger pair T1. The output of each gate is applied to the left-hand grid g1 of the associated trigger and to the right-hand grid, e.g. g21, of the next trigger. Initially, the first trigger is in the first state (left-hand tube conducting) so that a negative potential is applied to the gate A1, and when an input pulse is also applied to the gates, the gate A1 produces a negative output pulse which switches the first trigger to the second state and the next trigger into the first state. On receipt of further input pulses, only one gate at a time will produce an output. The associated trigger will be restored and the next trigger set to the first state. The end trigger may be connected to the first to form a ring. In a modification, Fig. 5, each switching circuit produces a negative output on receipt of a negative input pulse only when a positive potential is also applied thereto. This circuit is therefore connected to the anode all of the right-hand tube which is normally conducting, and comprises a rectifier N<SP>1</SP> connected to the input pulse supply and to a potential divider r15<SP>1</SP>, r152 arranged between that anode and a negative potential so that normally no current flows through the rectifier even during an input pulse. However, when the right-hand tube is non- conducting, the potential applied to the rectifier is raised so that current flows through it during an input pulse, and a negative pulse is passed through a condenser c6 to switch the associated trigger and also applied to the next trigger. A smoothing choke L is connected in the potential divider. In a further modification, Fig. 4, that trigger in the first state is switched as before but the next trigger is switched by a connection between the righthand anode, e.g. all, of the first trigger and the right-hand grid, e.g. g21, of the next. Each switching circuit comprises a single rectifier N having its positive terminal connected to the source t1 of negative input pulses and its negative terminal X connected over a resistor r16 to the left-hand anode of the associated trigger and over a resistor r15 to a negative potential. Normally, the rectifier N is non-conducting but when the left-hand tube of the trigger conducts, the potential at X is lowered and the rectifier conducts so that a negative input pulse produces a negative pulse at X which is passed over a condenser c6 to the left-hand grid g1.