At the present time, radar is taking a more and more important part in air traffic control. That part is certainly going to develop even further in coming years, with the steady increase of traffic and the general use of jets on main airlines. Radar control has the advantage of presenting the controller with a clear picture of the position of each target, associated with an instantaneous view of the whole air situation. And, because radar information is renewed several times per minute, the situation displayed is always up-to-date. Unfortunately, that situation is rather anonymous. To make it usable, the targets observed have to be identified. In the first place, we have information about them from the flight plans; the identification of a particular aircraft then reduces to a choice between a few possible echoes only. A commonly used method is to send an order to the target to manoeuvre: the target obeying that order identifies itself by doing so. This method is simple, but not very quick. Moreover, the ordinary PPI unfortunately does not retain a memory of such an identification.