The self-winding caliber AS 1654 is with a diameter of only seven lignes, which equals less that 16mm, one of the smallest self-winding movements ever made. It was launched round 1960 and is similar to the AS 1635, but with an increased beat rate.
As you can easily see, the small diameter requires some compromises, the maybe most notable one is, that the hairspring length cannot be regulated when the self-winding mechanism is mounted. But removing it is not a real challenge for an experienced watchmaker.
Due to the small diameter, it was required to build highly, which means, that the directly driven center second hand and the minute hand, which is also directly driven, like on classic movements, are located on top of each other. This classy way of construction leads to a thick movement, especially, since the self-winding plates mounted on top add quite a large amount of height to it. Since the movement looks a bit dull, the case designers had to work and ensure, that the big height was somehow hidden on small watches.
A specialty of the AS 1654 is the extremely tiny screw balance, which is secured by two Incabloc shock protection bearings. The balance doesn't beat with slow 18000 A/h, but already with top modern 21600 A/h, six "ticks" per second. This was a huge improvement for the accuracy, since these tiny movements were prone not to be ultimately precise.
How rare that combination of 21600 A/h and a balance with screws is, can be seen on the fact, that it it hardly used anywhere. The only other watch in my collection with that combination is the slightly larger Zaria 1800.
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