" At First, these wristwatches were a single-off or tailor made creations that often appeared a lot much like the pocket watches from which they progressed. But shortly, wristwatches took on their own aesthetic, with their particular complex innovations to resolve new problems presented by wrist-borne timekeepers. Exclusions could apply. https://www.watchesworld.com/a-history-of-watch-reference-numbers/