[Sidenote: _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. [Sidenote: _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. [Sidenote: _Forced simultaneity applied to a calculator impossible_] If you have ever watched an expert operator using a “Comptometer,” try to imagine that operator hesitating to select a group of keys and depressing them exactly simultaneously as one is compelled to do on one of the key-driven cash registers. And then, on the other hand, if you have ever seen a key-driven cash register operated, try to imagine its being operated at the lightning speed at which the “Comptometer” is operated.[4] [4] In making this comparison, the reader should be careful not to confuse the later key-set crank-driven type like that of Pottin described in the preceding chapter. It was the old key-driven type of cash register which contained the forced simultaneity of key-action. It must be understood that the exact or forced simultaneity of the cash register scheme, if applied to a calculating machine, would lock the whole keyboard if one of any of a group of keys the operator wished to strike was depressed ahead of the others, and would thus prevent the rest of the group from being depressed until the return of the first key. [Sidenote: _Flexible simultaneity of key-action a Felt invention_]