" At First, these wristwatches were being 1-off or personalized creations That always looked a good deal much like the pocket watches from which they developed. But soon, wristwatches took by themselves aesthetic, with their unique technical innovations to resolve new troubles offered by wrist-borne timekeepers. Launched within the 1940s https://www.watchesworld.com/a-history-of-watch-reference-numbers/