Our most nostalgic models are boldly reimagined with modern factors and familiar nods to our history of firsts. 100M Watertight: Having a water resistance of approximately 100M you can certainly handle most predicaments in life, including washing arms, rain, swimming(please tighten the crown when going into the water). YYZ, in https://www.watchesworld.com/a-history-of-watch-reference-numbers/