Review: Seiko Prospex Diver 300M Hi-Beat SLA025

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Whether you’re a WIS or just an avid watch enthusiast, there’s a high chance you’ve come across vintage watches. Love ’em or hate ’em, they’re not for everyone due to their delicacy. Thus, it excites us whenever a deserving piece gets rehashed and updated with 21st century technological innovations – especially from a distinguished brand such as Seiko.

Following last year’s release of the SLA017, the brand has chosen to mark the 50th birthday of its iconic 6159-7001 diver with another limited-production re-issue. The SLA025 is an über faithful homage to the 1968 diver, and is a piece that will tug at the heartstrings of “Seikoholics” and WISs alike.

Note that the SLA025 also exists under the moniker SBEX007. Both refers to the same watch, with the former sold in the international market and latter meant solely for the Japanese Domestic Market.


Review: Prospex Diver 300M Hi-Beat SLA025


Historical Considerations


The SLA025 is a modern re-interpretation of the 6159-7001 and was Seiko’s first attempt at a professional divers watch. Launched in 1968, it was the company’s third diver, succeeding the iconic 6217-8001 aka 62MAS and 6215-7001. The watch was well-ahead of its time, featuring a sturdy and distinct monocoque case design which allowed for an impressive water resistance rating of 300m – double of the 62MAS. And to ensure better accuracy and reliability, the 6159-7001 was equipped with a hi-beat Grand Seiko automatic movement running at 36,000 bph.

Sidebar: The term “high beat” (or Seiko’s derivative, “hi-beat”) refers to movements whose balance wheel oscillates faster than 28,800 bph. Benefits include higher accuracy and improved reliability.

Interestingly, the watch had a relatively short production span of only 2 years. Although Seiko remains silent on this, it is speculated that the watch, although surpassing its 300m water resistance rating during tests, was not sufficiently protected from shocks which resulted in popped crystals. Nonetheless, it laid the foundation for all future Seiko professional dive watches.


The Dial, Hands and Case


The SLA025 dons an attractive matte black “gilt” dial with complimenting gold-colored indices rim and minute track. “Gilt” is a term referring to the gold coloured printing on the dial and is favoured by collectors due to its vintage panache. The color matches the shade of the markings on the bezel, creating a look that is understated yet gorgeous.


The matte black “gilt” dial of the SLA025 is almost an exact copy of the 1968 model. The usage of gilt is a nice touch which adds vintage charm and charisma.


As a professional dive watch, functionality is prioritised amongst others with the dial being tidy and highly legible. The indices are filled with Lumibrite: a proprietary Seiko lume that provides a strong glow which lasts up to 5 hours. Additionally, unlike other offerings of the Prospex line, the dial does not feature the Prospex “X” logo – a tasteful design cue that contributes to its visual cleanliness.

Protecting the dial is a dual dome sapphire crystal with anti-reflective coating. The choice of sapphire in a tool watch is a natural one, given its durability.


The hands set on the SLA025 are a copy of the 1968 model, with a few modernisation tweaks.


The SLA025 also features a hands set which are a copy of the original. They are beveled and polished, and have been nicely executed. Also unlike previous re-issues, the “red dot” seconds hand extends fully to cover the indices. To ensure legibility, they are coated with LumiBrite.

Perhaps the definitive factor of any re-issued watch is their case. The SLA025 sports a hefty monocoque stainless steel case, measuring in at 44.8mm wide and 15.7mm tall – a tad larger when compared to the original. On handling the watch for the first time, its weight and robustness left a deep impression. Though it might be inundating on smaller wrists, the watch wore and sat rather nicely on the average wrist (6.5 to 7 inches in diameter) due to the short lugs. Decidedly, we’d prefer if the watch was made slightly thinner. The chunky case is accompanied by a tall uni-directional stainless steel bezel with black aluminium insert. Additionally, the watch also features super-hard coating for better scratch resistance, and the crown at 4 o’clock: a typical Seiko design cue and a faithful nod to the original.


A chunky and tall case, but one that still manages to wear nicely on the average wrist. Additionally, the fusion of Zaratsu polish and bushed surfaces creates a discreet yet brilliant appearance.


One interesting feature of Seiko’s professional divers are their Helium Escape Valve (HEV), which in place of a conventional HEV, utilises a specially designed L-shaped gasket and screw-down glass fixing ring to completely block out the gas. We’ve covered it in more detail in our review of the Seiko Marinemaster Professional 1000m Diver here.

Following the trend of recent mid-high end Seiko pieces, its execution is rather impressive. The case is an alluring fusion of sharp traditional Zaratsu-polished and brushed surfaces, giving the piece a brilliant yet discrete appearance.

If we were to nitpick, it would be that of its printed logo. It is frustrating to see Seiko not opting for an applied logo which would’ve brought it closer to the original. The same sentiments can be shared with other high-end Seiko re-issues such as the SLA017.

Turning the watch over, you’ll find a solid back that is engraved with “xxxx/1500”. The SLA025 is a limited of 1,500 pieces worldwide, and will come on a “waffle-style” black silicon rubber strap.


The Movement


Powering the watch is the Seiko caliber 8L55: a hi-beat automatic movement running at 36,000 bph. It boasts an impressive 55-hours power reserve, along with hacking and winding. The movement is handmade by elite watchmakers in the Shizukuishi Watch Studio, and has been used exclusively in several high-end Seiko divers. Given the nature of this piece, we felt that it was a natural choice.

Due to its monocoque case construction, the movement is inserted from the front. There is no clear case back or removable back for that matter.


The monocoque case construction results in a non-removable case back. Thus, the movement is loaded from the front.


The 8L55 is often touted as a less decorated and regulated version of the acclaimed 9S85 Grand Seiko caliber; industrialised and suited for usage in dive watches. The movement has an accuracy rating of -10/+15 seconds per day. Though not superlative in any aspect, our experience with Seiko movements would lead us to believe that the actual accuracy will surpass its rating once it “settles in”.


Competitive Landscape


The Seiko Prospex Diver 300M Hi-Beat SLA025 has a recommended retail price of ¥ 550,000. Rather steep, but neither is it the most expensive (the SBEX005 triumphs it with a retail price of ¥ 650,000). For its price, we get a remarkable hi-beat movement, superb case execution with excellent attention to detail and a limited-production watch.



Competitively, as a diver/tool watch outfitted with a high-beat caliber in its price bracket, there are no watches that would rival it. In fact, the SLA025 is the cheapest of its kind. Due to their complexity, only a handful of manufacturers currently produce high-beat watches. Conversely, if price wasn’t a limitation, it’d open up to more choices.

We start off with what is perhaps its most prominent alternative: the Grand Seiko Hi-Beat 36,000 Diver SBGH257. The entire watch is brilliantly executed with haute horology finishing and superb technical innovations. Decidedly, its case is rather massive with a size measuring 48mm by 17mm – part of which can be attributed to its impressive depth rating of 1000m. Powering it is the caliber 9S85: a refined version of the 8L55. In addition, the watch has anti-magnetic properties of 16,000 A/m. The Grand Seiko SBGH257 is priced at USD 9,800, and is limited to 500 pieces. A regular, non-limited version is also available, priced at USD 9,600.

Next, we propose the Blancpain Bathyscape Chronograph Flyback. The highlight of this watch lies in its movement: an in-house column wheel and vertical clutch flyback chronograph running at 36,000 bph. Sized at 43mm, the watch wears nicely on the wrist. In addition, with a 300m water resistance, it is a bona fide diver’s watch too. The watch is available in either a stainless steel or ceramic case, and is priced at CHF 13,800 or CHF 16,000 respectively.

Finally, we suggest the Rolex Sea-Dweller 126600. Launched during Baselworld 2017, the Sea-Dweller pays faithful homage to the original from 1967 with its “single-red” text on its dial, and has grown to become a fan-favourite. It is perhaps the most renowned and iconic dive watch in the world following the Submariner. Sized at 43mm, the watch wears rather comfortably on the wrist thanks to its short lugs and oyster bracelet. Furthermore, it is rated to a depth 1,220 meters. The watch is driven by the manufacturer caliber 3235, boasting an impressive 70-hours power reserve. There is no official word on its anti-magnetic capabilities. The Sea-Dweller 126600 is priced at SGD 15,520.




Though its thickness might detract some, we can’t deny the handsome looks and incredible movement this piece offers.


As with other Seiko re-issues, the SLA025 has been very nicely thought out. Almost every aspect of the watch is true to the original and one cannot deny its handsomeness. There is no doubt that its price tag as a Prospex watch will raise some eyebrows. But as we’ve discussed earlier, the SLA025 might be a value proposition to collectors looking for a robust high beat timepiece.


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1 Comment

  1. Just another guy on the web on

    Seiko is famous for vastly under-estimating the accuracy of its movements. Given the price and build-quality of tihs item, I am quite certain it would also deal with depths far in excess of 300m. Not that it matters. A superlative watch, which makes Rolex look frou-frou in comparison.