The “Volts/Div.” wheels amplify an input signal so that a division represents a certain voltage. A “division” is the distance between two lines of a square on the oscilloscope’s screen.
A setting of “.5” i.e. means, that the height of a single square equals a voltage of 0.5 V. An amplitude of 1 V would have a size of two divisions vertical to the abscissa.
The “Volts/Div.” wheel is made up of two wheels.