Though I agree with what has been written, to keep things in context, let's recall that the core of an altimeter is an absolute measuring instrument. It measures a pressure effect upon sealed cells, which are temperature compensated. It has no idea what the pressure nor altitude is, until you tell it.
You adjust the datum for the altitude measurement, which might be set as the altitude you know to be that for the altimeter, or the subscale pressure. (By the way they can be set relative to each other, but don't do that, unless you are so authorized - when you drop the screw to your surprise, and can't get it back in, even if you do find it, the maintainer will know you had it apart!)
With the altimeter in "operating" mode, when you turn the setting knob, you turn the entire altimeter mechanism inside the case (it'll go around as many times as you want), and you turn the subscale by gearing (it will not go around endlessly).
So your setting the altimeter subscale or altitude, does nothing other than to move the instrument datum to where it should be - it has zero idea of either value, beyond what you tell it, other than it keeps track of changes once you tell it.....