Zener Diode with LED for Collector Voltage Indication

[Phend]

Hello:
Looking at a Fuzz circuit biasing of transistors collector.
A Fuzz Face for instance, some modified circuits include a trim pot or even an external pot to change the resistance to the collector.
Question: Has anyone used a 4.3v or 4.7v Zener / LED in combination with a pot to indicate when the pot is setting at said voltage(s) ?

Edit: I see this is not possible, tested on a BB the led just goes from dim to bright when 10K pot is turned from min to max. More components would be needed to turn it OFF at 4.7 or 4.3 volts.

[FiveseveN]

Look for "window comparator".

[antonis]

Look for "window comparator".

With ot without hysteresis..??

[Phend]

Maybe sometime I will try the Window Comparator, but for this build I will use a simpler method, "dial" in 4.5v and make a mark on the effects face plate. Guess I could make marks 0 to 10, get fancy.  I inserted a "plug in" for a resistor selection to add in front of the pot (10k) so I can tweak that to get 4.5 at 5. But hey, I did learn something about zener and windows today.
Thanks

[antonis]

Honestly, never dealt with FFs but I always though that they are trimmed by ear..