I have a guitar. It has a knob that makes it go quieter and louder. It also has a volume control.

You have more than one guitar, Jim, I'm sure of this - so don't try to hide your anorak under a bushel (or some other tortured metaphor).
OK... you asked for it...
I have:
A 1980 Gibson Les Paul Standard with Gibson Alnico humbucker pickups
A mid 90s Fender Stratocaster with standard Fender pickups and a Floyd Rose locking tremolo
A Squier Stratocaster with retro fitted EMG SA active pickups (for that genuine David Gilmour/Steve Rothery chiming clean sound).
A Variax 300. Not sure what I can tell you about this without using all the pages this forum will ever be allowed. It's amazing.
A mid 60s Marshall 100 watt solid state amplifier. This was one of the first solid state amps Marshall ever made and somehow, they managed to build into it all the warmth you would expect from a valve amp. It simply sings when put through my...
Mid 60s Marshall 4x12 angled speaker cabinet, tweed fronted with 4 Celestion vintage c30 speakers. Both the amp and cab used to belong to Tom Robinson ("2, 4, 6, 8 never too late" for those who don't know who I'm talking about). It was given to me by a friend who needed to clear some room at home. He tells me that this amp and cab combination once appeared on the front cover and in a feature "article" of specialist gentleman's one-handed rhythmic reading journal, Razzle. A friend of his is a glamour photographer and was doing a "British Rock Chicks" shoot for said publication. My chum went along and spent more time there than is strictly healthy for a) a married man and b) a Police Officer.
All this lovelyness is shaped and molded by the addition of:
A Line 6 X3 Pro, Amp modeling pre-amp and effects unit. This too would take too much space to talk about but aside from my Les Paul, this is the best and awesomest piece of equipment I have ever used.
A Line 6 XT Pro (the little brother of the X3 Pro)
An Alesis Midiverb
An Alesis Quadraverb
A Roland Guitar synth unit
All of these are controlled from a Line 6 FBV longboard pedal board and foot controller which has a built-in Wah and Volume pedal. This too is a miracle of modern technology and engineering.
Lastly, why did no one spot the deliberate attempt at self-depreciating humour in my original post about the knob and the volume control. Or was it just too oblique for a Sunday morning?