The Vertical Amplifier
In a typical cathode ray tube, the vertical deflection plates require
approximately 100 volts between them to deflect the spot by about 20mm.
As most voltages we wish to measure are considerably less than this, the voltage is applied to the deflection plates through an accurately- calibrated amplifier.
The selector switch on the front panel of the oscilloscope allows us to select a suitable setting to provide a good deflection on the screen regardless of the actual voltage.
The switch positions are marked in Volts/Division and in the picture is set to 1 volt/division. Therefore the waveform shown in the lower picture is approximately one volt between peaks (1v peak-peak).
The control at the top-left of the panel allows the display to be shifted vertically on the screen in order to more accurately align the waveform with the grid lines.