"Interest in the human-operator problem was stimulated by Prof. Arnold Tustin of the University of Birmingham, England, who suggested the application of the delay-line synthesizer to the study of some tracking records which he had brought with him from England. His experimental setup from which data were obtained consisted of a movable handle unit whose output was integrated once and then made to position a mechanical pointer. A second pointer, located next to the handle-driven pointer, was given an input motion consisting of a number of sinusoidal components of a nature sufficiently involved to prevent anticipation by an operator. The operator, upon noticing an error or difference between the two pointers, was required to move the handle in such a way as to reduce this error to a minimum value..."