The scope uses a sweep generator which sweeps from negative x-axis to positive x-axis. The sweep generator used in this circuit is sawtooth wave. The sweep generator controls the horizontal plates of the scope and deflects accordingly.
The signal to be plotted is applied to vertical plate which deflects the electron bean vertically.
This is how a scope operates in Y-T mode.
To change the time/div the frequency of the sweep generator is changed.
To change the volts/div the amplitude of sweep generator is changed.
Btw the above circuit operates in XY mode.
To get Lissajous patterns the a different signal is applied in horizontal plate.
