“Each individual brand tried to have logic within their numbering method but unsuccessful miserably,” Mandelbaum continued. “It just signifies the overall absurdity from the Swiss trying to think of a numbering system. 100M Waterproof: By using a h2o resistance of approximately 100M you can certainly take care of most predicaments https://www.watchesworld.com/a-history-of-watch-reference-numbers/