Lose track of time underwater, and you could lose your life when your oxygen runs out. Luckily, the Eterna KonTiki Diver watch saves you from your own absentmindedness. It uses technology from the automotive industry to stay waterproof at 3,280 feet without tightly screwing down its winding stem (a step that users often forget with other mechanical diving watches).

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I believe in the latest issue popsci listed this watch as costing $ 18,000 i think the thousands one saves by simply remembering to properly prepare there normal diving watch is enough to help remember.
There is a guy here in the UK that sells a deep ocean watch
not only for 200ft deep oceans. But it reqires no maintenance for 30 years,guaranteed.
He charges £600. for taking a Casio 'Wave ceptor' with a Solar face (never needs a battery, and gets its time from
the World Radio )
Strpis it down to the basic mechanism, and fits it between two H tensile convex glass 1.5 inch diam slips, that look like this with the watch in the middle (). I believe the edges are sealed with a clear resin. It looks really beautiful and modern.
It fixes around your wrist using a nylon 'hook and eye' strap,
but for £600 with nothing to adjust ever, who cares