Hands-On The Seiko Prospex SPB451 And SPB453

With the looming threat of the dreaded sophomore slump, it's worth considering the recent roots of the SPB453 – don't worry, I promise to be brief. This specific generation was announced in March of this year as a trio of references – the SPB453 (black), SPB451 (blue), and the limited edition SPB455 (black with gilt accents). All three represent a retooling of the so-called "20MAS," which was the 2020 aesthetic re-edition of Seiko's first dive watch, the 62MAS.

Though the 20MAS line would grow to include a wide variety of colorways for the design, the core of the range was the grey-dialed SPB143. I was, and remain, a huge fan of the SPB143, and I think it represents one of the best models Seiko has released in the past several years. I wrote a lot about it, and some of the context for this hands-on will build upon concepts established in my Week On The Wrist with the SPB143.

For this new trio of 24MAS divers, Seiko largely stuck to the same playbook while taking the liberty to tweak a handful of elements core to the design. The changes to the new models include slightly smaller cases, a new date position, a new movement, and a redesigned bracelet.

Seiko now lists the case dimensions as 40mm wide, 13mm thick, and 46.6mm lug to lug. When I measured with my own calipers, I got 40.2 x 13.4 x 46.6mm. The lugs remained drilled (amazing) and fit the bracelet's 20mm end links. The caseback remains a closed steel format, but thanks to a new design, water resistance is now 300 meters (compared to the 200m offered by the previous generation).

For the bracelet, the design tapers to 18mm at the clasp and features shorter links and a smaller clasp to allow for a more comfortable wrap of your wrist. The case and bracelet both feature Seiko's "super-hard" coating, the bezel uses an aluminum insert, and the crystal is made of sapphire.

From a spec standpoint, these new divers use Seiko's 6R55 movement. It's an automatic movement that offers 72 hours of power reserve (hence the "Automatic 3 Days" on the dial) while ticking at 21,600 VPH. This movement is largely similar to the 6R35 in the previous generation, and I've included a look at its accuracy below.

The final considerable change over the previous gen is a dial redesign that opts for more conventional colors/textures while also moving the date from three to 4:30. The date is a truly divisive thing, and while I'd always recommend that a company the size of Seiko just also produce a no-date version, I think they'd made the most out of the push to 4:30. You now get a full-size marker at 3, and Seiko says that was an element of the decision to move the date, better adherence with ISO 6425 (this is why they also started adding a luminous marker into later versions of the original spec).

Be that as it may, 4:30 dates are treacherous. Here, Seiko has opted to at least respect you in the process, as they've designed a date display that is unobtrusive and has its font aligned with the rest of the font on the dial. It's not perfect, but at least we see attention and forethought. So many 4:30 dates feel like an afterthought, like a casual hole punched in a dial to offer a view of a date wheel that was designed to display at three o'clock.

Not here. The SPB453's date is legible and otherwise completely ignorable. On the blue dial SPB451, the date wheel is black (rather than blue), which is a weird choice, but you have to look very closely to even notice as the aperture is so small and is almost always seen in shadow. It's a compromised solution, but not one that would be a deal breaker for me. But again, offering a no-date has a proven track record.

So, on wrist, and I'm sure some of you can see this coming, the SPB453 wears very very similarly to the SPB143. And that's not a bad thing (like, at all). The updates to the bracelet definitely make it more comfortable, and the now-conventional black dial and bezel offer excellent legibility and the sort of lume you want from a Seiko dive watch. The bezel and crown both feel nicely made. The bezel has a heavy action with a light click and good alignment with the dial markings (though it can sometimes look askew given the depth of the dial vs the depth of the bezel).

Basically, if you're happy with how the SPB143 wore, I can't imagine a wrist where this new generation isn't just a bit more comfortable – but the presence is largely the same. Take it from the guy with three younger brothers, it's a blessing to have a handsome, successful, and widely-loved older brother. As a Seiko dive watch, the SPB453 has the same goals as its older siblings and benefits from being able to respond to the success of the 20MAS. 

Being so similar to the SPB143, the other element at play here is timing, as competition is hotter now than it was in 2020. The SPB453 (and its siblings) carries a list price of $1,300. Back in 2020, you could get the SPB147 on a rubber strap for $1,000 (and the SPB143 on bracelet was $1,200). And while I'd argue that this pricing is fairly standard for a watch of this caliber over the past four years, the SPB453 doesn't offer some of the special features that we have seen become more common in recent years.

I'm talking about quick-release for the bracelet or tool-free micro adjust for the clasp. Heck, I'm a diver, and I'd still definitely trade the dive-friendly wetsuit extension (which the SPB453 does have) for an everyday friendly micro-adjust in the clasp. As it stands, the new clasp only offers two micro-adjust positions. For those who have asked, the minimum bracelet size capable for these new models is 11.1CM (4.37 inches) with all of the links removed. It's mostly clasp and case at that point.

I know it seems like I'm picking on the bracelet, but let's be clear: I am exceedingly picky when it comes to bracelets, and I almost never wore my 143 on the bracelet. Seiko did a great thing by re-tooling this bracelet for better wearability, but it still feels a lot like a more sturdy and refined version of a bracelet you might have gotten on a Seiko 10 years ago. The wetsuit extension is exactly like that on my Orange Monster's bracelet, and the links use pin-and-collar construction, even in an era when boutique brands offer single-sided screwed links (not to mention quick change and micro-adjust) in bracelets for watches that cost less than $1,000.

This helps explain two points. First, Seiko should offer a version on a rubber strap for $999. It would sell, and these cases are incredible on straps. Second, If you're going to refresh a bracelet, give it all the goodies that are becoming more and more popular at this price point.

Now, let's address the number one question I got while I was focusing my efforts on the SPB143 a couple of years ago – the accuracy of the movement. While my SPB143 was a fairly accurate example, you don't have to Google all that hard to find folks who had some trouble with their 6R35 or similar not keeping great time.

While I only really care about a watch's accuracy to the point where I don't notice it being fast or slow, this is a crucial aspect for mechanical watches, and it's not 2007 anymore; people aren't paying $110 for a 7S26-powered Seiko that keeps iffy time. As such, while neither the SPB453 nor 451 triggered my own mental accuracy threshold, I did put both of them on a timing machine. This data is anecdotal, to be sure, but these are early examples that came directly from Seiko.

My timing method was to measure over six main positions and three phases of wind (full, after 24 hours, and after 55 hours). This gives us 18 measurements for accuracy across the six positions and at three stages of wind, which feels like a fair (if brief) gauge. For the SPB453 (the black dial), the six-way average for the three phases was -5 s/d (full wind), -12 s/d (less 24 hours), and -15.8 s/d (less 55 hours). For the blue dial SPB451, I got -4 s/d, -6 s/d, and -11.8.

That means that over the course of a full wind, the SPB453 averaged at -10.9 s/d, and the SPB451 averaged -7.3 s/d. Given that Seiko says that the 6R55 is accurate to -15 to +25 seconds a day, both of these watches fall within the stated range of the movement, but both were running on the slow side of zero. I will venture a guess that Seiko regulates these movements in dial-up or down positions, as both were significantly more accurate in those two positions.

How much those numbers weigh into your buying decision is a subjective concept. For me, neither would keep me from getting a watch that I otherwise very much like. Nevertheless, I do think that Seiko should restructure how it manages and ensures the accuracy of its movements as competition has increased at the price point, and more of the major players (of which Seiko can be included) have started to push for more brand-led consideration of accuracy.

All told I have been thinking of this new 24MAS generation as though it's the follow-up album from a brand that had a killer debut. Seiko is the label, the band is the 20MAS-style watch, and the SPB453 (and its siblings) form the highly anticipated sophomore album that has to deal with the cult-like success of the first album.

The SPB453 will be entirely recognizable and comfortable to anyone who knows the SPB143 (or similar). Sure, you may not love track #8 "We Moved the Date Window," or maybe you find the album to run a little slowly at times – but it's still a tight collection of Seiko dive watch themes layered in a manner that makes for the sort of watch you can't stop wearing. No, it's not perfection. But hey – that took Pink Floyd nearly 10 whole albums.

Seiko had quite a challenge in returning to the drawing board to improve the SPB143 without spoiling any of what made it so good. For the SPB453 (and similar), I think they did a largely great job in tweaking the execution without missing the core message. It's still a handsome, solid, and tool-ish everyday dive watch that does a great job of not messing with what was already working.