" At The beginning, these wristwatches had been one-off or tailor made creations That always appeared a good deal similar to the pocket watches from which they developed. But soon, wristwatches took on their own aesthetic, with their particular complex innovations to unravel new difficulties presented by wrist-borne timekeepers. Weiss https://www.watchesworld.com/a-history-of-watch-reference-numbers/