Seiko celebrates its 140th anniversary in 2021 with several special models. In addition to the modern reinterpretation of the Prospex Diver watch from 1970 created for explorer Naomi Uemura, there is also a non-limited version of the world-famous diving watch that we tested.

In contrast to the limited edition, the non-limited version of the Seiko Prospex model, our test watch, has a charcoal gray matte dial, just like the original from 1970. By setting the date at Between the 4 and 5 o’clock positions, the bold 12 can be applied with a double-bar hour marker at the 12 o’clock position for perfect orientation.

The hour and minute hands, second hand tips and indexes are all generously coated with Lumibrite, Seiko’s own luminous material, to ensure optimal legibility at night. The orientation point on the diving bezel seems to consciously occupy a rearward position. The unidirectional bezel, in the same gray color as the dial, clicks in half-minute increments and is engraved to the minute. It surrounds a domed crystal with an anti-reflective coating on the inside, contributing to overall excellent legibility and scratch resistance.

The hard coating on the alternating polished and brushed surface of the asymmetrical case, widely used on Seiko diving watches, helps protect against scratches. The recognizable crown is screwed inside the ergonomic, uniquely shaped crown guard at the 4 o’clock position. But removing the crown takes a lot of strength, and pulling it to different installation positions requires strong nails; Getting the crown to the down position also requires some effort. However, the action provides a solid sense of security and the water resistance that Prospex offers to a depth of 20 bar. The sturdy threaded back adds to this sense of security. It is engraved with the image of a giant wave – the symbol of diving watchmaking.

Prospex is also known for its movement, a caliber specifically designed for use in professional diving watches. The automatic 8L35 movement is housed beneath the sturdy case back. It has its origins in the Grand Seiko Caliber 9S55, introduced in 1998 (after a 20-year hiatus) as Grand Seiko’s first mechanical watch movement. Caliber 8L35 appeared about two years later – specially modified for diving watches by the watchmakers at Shizukuishi Watch Studio Morioka in northern Japan and, like the Grand Seiko movement, assembled and adjusted by hand.

The 8L35 consists of 192 components and ticks at 4 Hz with a power reserve of over 50 hours. Broadly speaking, this is a less refined version of the Grand Seiko 9S55 caliber with a larger balance wheel to manage the torque needed to advance the giant diving watch hands. And, regarding the rate claims, we find that the 8L35 is not held to the same standards as the Grand Seiko caliber. To ensure the accuracy of the 8L35 watch movement, the manufacturer states that the error range is +/- 15 seconds per day. The movement in our test watch remained within these specifications with a deviation of 6 to 7 seconds per day.

The Prospex is worn on a five-row integrated steel bracelet, whose clasp is equipped with a safety bar and a sturdy diving extension. It’s easy to see why this watch has been the professional underwater companion for more than half a century.

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