Using an analog voltmeter to display the changes in out put made by a dimmer switch for a light
if you just want a "a different reading" depending on how the dimmer is set, just connect a simple AC voltmeter in parallel with the lamp,

With SCR type dimmers the voltmeter will not accurately track the amount of power going into the lamp but it will casnge according to the dimmer setting.

basically you put a bridge rectifier around the movement of a dc voltmeter and put a high voltage resistor in series with the input, be sure to insulate everything well.

these ones have that construction internally, 

https://www.aliexpress.com/item/300V-AC/32954665170.html

With a 300V range they are well suited to 230V operation, but for lower voltages the needle won't visit most of the scale, they can however be opened and modified - eg: you could reduce the resistor to make the needle travel further