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This paper describes three different types of automatic-frequency-control circuits: (1) sawtooth type, (2) sine-wave type, and (3) pulse-time type. The sawtooth system forms a sawtooth from the pulse present across the deflection yoke. This sawtooth is compared in phase with the synchronizing pulse to produce a control voltage for frequency phase control of the sweep circuit. The sine-wave type comprises a stable sine-wave oscillator which is controlled in phase and frequency by the synchronizing pulse, and in turn controls the sweep circuit. The pulse-time system measures the area of the synchronizing pulse as it rests on the edge of a shelf. Phase variations change this area, and provide information to control the sweep circuit.