You know? It's really hard to write about a puzzle when the meta mechanism is supposed to be a puzzle.
This one shouldn't be too hard because .... well, I think it's cute.
ERRATA: Oh, screw! There is a fairly serious error in the mechanism. However anyone who gets that far should clearly see what I was intending. So if you get an answer but it's just off by a little bit, enter the slightly amended not quite correct but sensible answer. That will be the right one.