It's much weirder than that: you can close and open the vernier in a particular fashion (very slow and then very fast, it's an art) and keep adding 5.08mm in quantum steps: 5.08, 10.16, 15.24. The largest value I got on a boring day was around 200mm, on a 150mm vernier.
I'm kinda surprised it doesn't self-reset when closed and then opened fully. That would be a very easy way to automatically 'fix' any location ambiguity with software-only changes.
