a sweep of a cathode-ray oscillograph that is triggered only for the duration of the electrical process being observed. A driven sweep is triggered either by a command given by the device that controls the appearance of the process (for example, by the timer of a radar set) or, with spontaneous initiation of the process (as in a lightning discharge), by the process itself. In the second case a delay line is used to observe the initial part of the electric process, which precedes the triggering of the driven sweep. The delay line accomplishes a time shift of the entire process before displaying the process on the screen of a cathode-ray tube.