Besides the redistribution of mechanical functions, another very noteworthy feature is found in these patents which, in the specific means disclosed, constituted another distribution of time for mechanical action. This in the capacity of the machine was what has become commercially known as the “Duplex” feature.
In the old “Comptometer” it was necessary to operate the keys alternately, as a carry from one order to a higher order might be taking place and thus be lost in the action of the higher order wheel while rotating under key-action.
Multiplex key action
In the machine of the later patents the carry was delayed while the higher-order wheel was under key-action. The construction shown consisted of a latch operated by the actuators, which, when the actuator was depressed, latched up the delivery end of the motor carrying-device so that a carry due to take place at that time would be intercepted until the actuator returned to normal again, at which time the carrying motor device was again free to deliver the carry. This feature allowed the striking of keys in several or all the orders simultaneously, alternately, or any way the operator pleased, which was a great improvement in speedy operativeness.
Control of the carry by the next higher actuator
While the genus of this elastic keyboard invention consisted of control of the carry by the next higher actuator, the specie of the generic feature shown was the delayed control. The first production of this generic feature of control of the carry by the next higher actuator that gave the elastic keyboard-action is shown in the two Felt patents.
It may be argued that this new keyboard feature was simultaneity of key-action and that simultaneity of keyboard-action was old. True it was old, but the flexible simultaneity was new and depended upon individuality of ordinal control for its creation, and Felt created the ordinal control that gave the flexible keyboard.
Simultaneity of key-action was old in key-driven cash registers; such invention as had been disclosed in this line, however, would defeat the usefulness of simultaneity in a key-driven calculator. The useful feature of depressing keys in several orders at once in a key-driven calculating machine lay only in the increased speed of manipulation that it could offer.
Forced simultaneous key-action old
Now such simultaneous key-action as had been invented and used on cash registers was not designed with the thought of increasing the speed of manipulation in such machines. The simultaneity of the cash register was designed to compel the operator to depress the keys, which represented the amount of the purchase, exactly simultaneous; otherwise, by manipulation the proper registration could be made to show on the sight-register and a short amount on the total-register. It was a device to keep the clerk or salesman straight and prevent dishonesty.