The observation of a radar display by a human operator leads to the establishment of aircraft tracks. These tracks are subsequently used by the controller. More and more often, it is proposed to replace both PPI display and human observer by an automatic computer, either special or general purpose, to perform tracking.

In the present paper the basic performances of these two modes of operation are examined, taking into account the psychological and physiological features of human vision and hence the mental association of the viewer. The computer is more precise, but more costly and, when saturated, the drop in performance is abrupt. The number of tracks handled by a human operator is small, but the brain is very versatile and works very well in confused situations, with a slower drop in efficiency than the computer.