The ETA 2551 is the selfwinding brother of the caliber 2541. With a diameter of only 7 3/4 lignes it is a truely tiny ladies' watch movement, which is also feature-rich. It offers the well known and almost two decades familiar bidirectional winding system as well as a fast switching date mechanism, which can be corrected semi-fast.
Compared to its predecessors like the ETA 2365, you see, that it was produced a little cheaper. The "click spring" of the winding system is now just an ugly kind of wire and the screw balance was replaced by a simple three-leg screw-less balance.
As usual, this ETA movement also contains an (hidden) yoke winding system and an indirectly driven minute hand, which allowed a significantly larger diameter of the balance and thus a higher precision.