A gears-level model is 'well-constrained' in the sense that there is a strong connection between each of the things you observe-- it would be hard for you to imagine that one of the variables could be different while all of the others remained the same.
Related Tags: Anticipated Experiences, Double Crux, Empiricism, Falsifiability, Map and Territory
The term gears-level was first described on LW in the post "Gears in Understanding":...