Since SEIKO sold its first diver’s watch in Japan in 1965, it has been a pioneer of diver’s watch standards for the ISO (International Organization for Standardization) and JIS (Japanese Industrial Standard). What is a “standard diver’s watch” for SEIKO? The 300m saturation diving waterproof specification, one of the measures of professional divers, was assumed and a one-piece structure where the movement was inserted from the top of the watch was adopted. There is no plate on the back side, which reliably eliminates one “part that needs to be opened and closed” that leads to the risk of exposure to water and also decreases the risk of the watch being caught on a diving suit. The rotating bezel is fixed by a separate screw clamp at the lug base, which increases convenience of maintenance. Concavities and convexities on the urethane band ensure that the watch tightly fits the wearer’s arm, which thins due to pressure while diving. This system was also developed by SEIKO and is now an icon of the diver’s watch. Though the band of this model is seemingly simple, the shapes of both the upper and back sides were scrutinized and greater stretching properties than what there appeared to be were realized. Subtly wide and powerful, the overall volume of this watch is modern.