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Seiko Prospex Marine Master 300M Blue Dial Ref SLA023

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At A Glance

Brand | Seiko

Reference | SLA023

Movement | Calibre 8L35

Model | Prospex Marine Master 300M

Strap | Bracelet

Crystal | Sapphire

Style | Dive Watches

Case Width | 44mm

Case Height | 15.4mm

About This Watch:


The Seiko Prospex Marine Master 300M Ref SLA023 continues Seiko’s rich dive watch history with an aesthetic design that is reminiscent of early 6215 models.  Modern updates include a ceramic bezel, a sapphire crystal, a monoblock case, and a Calibre 8L35 movement.  

The History:  Seiko first entered the dive watch market in the 1960s after a request from a local diver to build something that could hold up during deep sea dives using diving capsule & saturation techniques.  His complaint was that most watches would malfunction and become damaged upon reaching greater depths.  The answer to this request was for Seiko to establish a development team to design a timepiece that could perform reliably under the extreme conditions of deep-sea diving, and they did so magnificently.

The Watch:  One of the most notable characteristics of the Prospex Marine Master SLA023 is the monoblock case that is polished using the Zaratsu Polishing Technique, which is a mirror blade polishing technique performed at the Grand Seiko manufacturing facility.  The case is then treated with Seiko’s DiaShield coating to prevent scratches during wear.  The SLA023 has a sapphire crystal and features a Caliber 8L35 movement based on Grand Seiko’s 9S55 movement.  The blue dial features a sunburst pattern with brushed metal hands that are filled with Seiko’s own Lumibrite luminescence composition, as are the number plots.  A date window is featured at the 3 o’clock position.  The SLA023 has a 50-hour power reserve and a water resistance rating of 300 meters.

The Details:  This Seiko Prospex Marine Master 300M SLA023 is in very good condition.  The case and crystal are in excellent condition, and the stainless steel bracelet has slight wear markings on the clasp, which are visible in the photos.  This timepiece comes with an outer sleeve, inner and outer boxes, instruction manual, manufacturer warranty booklet, warranty card, registration booklet, hang tag, and additional rubber strap.
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