Why is that essential? If a unidirectional bezel is knocked and unintentionally moved on a dive, it can only Exhibit an extended underwater time. Which means the wearer will overestimate rather then underestimate immersion time, As well as in conditions that involve decompression stops, this can be a make-it-or-split-it issue https://www.watchesworld.com/frozen-in-time-luxury-watches-for-winter/