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Read and learn Loosegoose..>>>>>>><<<<<<<<..https://en.wikipedia.org/wiki/Nautical_mile

Astronaut Colonel William Pogue wore a yellow-dial Seiko ref. 6139 on his Skylab link 4 mission in 1973, making it the first automatic chronograph to travel to space. Because link of this, it's become one of the most collectible vintage Seikos and also something enthusiasts are always demanding a reissue of. The defining features of the "Pogue" link are the red-blue bezel and vibrant yellow dial (for real nerds, Colonel Pogue wore a 6139-005 "Resist" model).

They addressed this very specific problem by introducing the 6159-7010. It took 20 patents and link an unconventional approach to create the watch. Rather than incorporating a helium release valve like some of link its contemporaries the 6159-7010 never let any helium in the watch link to begin with. It accomplished this through specially designed gaskets and seals. Again water resistance doubled and the "tuna" as it became known was water-resistant to 600m.