A feature worthy of note connected with this change is displayed in the method in which Felt overcame the timing of the stop action of the actuators in the downward action they received from the keys, which would have been as hard to control as it was to control the wheels under direct key action. [Sidenote: _Alternating stop scheme_] The scheme he devised gave more than double the time to perform the function of intercepting the lightning action with which the actuators moved under a quick key-stroke. The scheme shows a dual alternating stop-action constructed by the use of two stops acting at different levels and co-acting alternately with five equi-spaced stop-shoulders on the front end of the actuators, which were also arranged in different levels. The two stops were actuated by the keys in a similar manner to the single stop which co-operated with the pins of the wheel in the old “Comptometer,” except that the odd keys operated one stop while the even keys operated the other. Thus in the new “Comptometer” the (1) key acted to throw the higher level stop into the path of the lowest stop-shoulder on the actuator, and the (2) key acted to throw the lower level stop into the path of the same stop-shoulder on the actuator. In the same manner the (3) and (4) keys caused the odd and even stops to engage the next higher stop-shoulder on the actuator and so on with the rest of the keys. As the spacing was doubled by the use of but five stop-shoulders, the stops were allowed double the time for entry between the stop-shoulders plus the space that the pin occupied as compared with former method, which was considerably more than double the time allowed for the same function in the old machine. 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. [Sidenote: _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.