let's imagine for an instant that the number for the hour is painted only on the right part of the small disk where it is painted now (now it is right in the middle of the small disk), and the left part is masked with a semi-disk above it. when the number is up right, we see that one only.
When the number is upside down, it is on the left side of the disk and hidden behind the semi disk. the dial would only show the current hour, up right and in its right place. all other ones which are upside down would be hidden.
(food for thoughts, for a version 2, may be...).