Example of discrete variable?
a variable resistor is often called a control potentiometer
,
and would be used to supply a set voltage depending on the
position of the wiper contact on the resistor assembly .
........
an example would be a speed control device on a motor ,
including battery drill drivers , a mini hand held drill tool for
use in craft projects , a volume control slide/ positioner , which
controls the amount of signal and hence the volmue at whic music is
played on a music system throu speakers.
it could also be used in lighting control circuits , such as
dimmer controls .
where it sets the level of light output by varying the applied
volatge to the lamp