Review: The New Grand Seiko Kodo Constant-force Tourbillon SLGT003

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In 2020, the world bore witness to something off the beaten path from Grand Seiko: an openworked, concept movement which incorporates a constant-force mechanism and a tourbillon as one unit on a single axis. This was the T0 Constant-force Tourbillon concept movement. While impressive, the T0 was an uncased, unwearable movement; it was not a wristwatch, let alone a sellable wristwatch. For Grand Seiko to turn the T0 into something more, significant miniaturisation and redesign would be required. And that’s exactly what they did.

Grand Seiko Kodo Constant-force Tourbillon SLGT003

Enter the Kodo, Grand Seiko’s most complicated mechanical wristwatch ever. The release of the Kodo was a huge deal for Grand Seiko, for it brought with it many firsts: first mechanical tourbillon, first constant-force mechanism, and first skeletonised watch, among other achievements. Introduced at Grand Seiko’s debut appearance at Watches & Wonders Geneva, the significance of the Kodo and what it means to the brand cannot be overstated. Here, we bring you the details and our honest thoughts on the most epic Grand Seiko timepiece ever made.

The Case, Dial, and Hands

The case of the Grand Seiko Kodo Constant-force Tourbillon SLGT003 measures a contemporary 43.8 mm x 12.9 mm. It is constructed from both 950 platinum and the brand’s Brilliant Hard Titanium with longevity in mind. The idea is that the harder titanium alloy protects the softer platinum alloy within. This also plays well with the theme of ‘light and shadow’ that Grand Seiko is going for with the Kodo. The two alloys combine most evidently at the tapered end of the lugs, with the titanium alloy appearing a darker shade of grey than the platinum. The small space within each lug gives it a skeletonised appearance that complements the skeletonised movement. The finissage applied to the case is gorgeous, done by hand, and alternates between mirror polishing and satin finishing for maximal contrast.

The design of the lugs echoes the airiness of the movement within.

The case, as beautiful as it is, serves only as a prelude to the main act that is the dial (or what’s left of it anyway). Indeed, hardly anything you see on the face of the watch can be considered dial, save for the skeletonised hour and minute track at 12 o’clock. On it are incredibly well-finished, multi-faceted hour markers. The time in hours and minutes are indicated by two hands of substantial thickness and finishing, as evidenced by the prominent beveling and polishing. There’s also a power reserve display at 8 o’clock. If you want to be nitpicky, that is, by definition, the only complication (a function other than timekeeping) the watch has. However, that’d be quite an injustice done to the crazy looking contraption at 6 o’clock, the very soul of the Kodo. What you’re looking at is actually the tourbillon and constant-force mechanism combined co-axially. It’s rare enough to find a wristwatch with both devices, let alone one with the two integrated as one unit on a single axis. It might not be a classical complication, but it is a smart mechanical creation that improves chronometry. We’ll just say it’s a technical complication and call it a day.

The strap that comes with the Kodo looks like but isn’t stingray. It is 100% calfskin treated with Urushi lacquer.

The Movement

Driving the Grand Seiko Kodo Constant-force Tourbillon SLGT003 is the Calibre 9ST1. Derived from the T0 concept movement from 2020, creating the Calibre 9ST1 was more than an exercise in miniaturisation – the majority of the components from the T0 had to be redesigned and reengineered for production. The power reserve display, for example, has a different orientation in the Calibre 9ST1 compared to the T0. The movement has a power reserve of 72 hours (but with 50 hours of constant force) and operates at a modern 4 Hz beat.

The Calibre 9ST1 as seen through the sapphire crystal case back.

The highlight of the movement is, of course, the co-axial tourbillon and constant-force mechanism. From above, the first structure you see is the bridge that supports the carriages of the constant-force tourbillon. Immediately below said bridge is the constant force carriage which jumps once every second to complete a full rotation in one minute. This carriage has three arms, one of which is marked with ruby to display jumping seconds. And just under the constant-force carriage is the tourbillon carriage which spins smoothly to also complete one rotation in one minute. Superimposed, you will see three arms jitter as three other arms pass smoothly – a sight to behold and not something you often, if at all. The constant-force tourbillon as a single unit serves to reduce gravitational effects on and fluctuations in energy supply to the balance, thus improving chronometry.

The star of the show. The co-axial constant-force tourbillon occupies much of the movement space and provides a grand spectacle.

From an aesthetics point of view, the Calibre 9ST1 is unlike any Grand Seiko movement ever made. It is the first and only openworked movement from the brand. Whatever material that isn’t essential for structural integrity or function is pared down, giving observers unparalleled visibility of every movement component. Improvements in movement finissage have also been made in the making of the Calibre 9ST1. Unlike in most Grand Seiko models which are more mass-produced, there is a significantly greater degree of hand-finishing involved here. Our favourite aspect of the finissage is the polished bevels. There is a good mix of flat and rounded bevels on every edge, of which there are many, because skeletonisation increases the number of facets on the parts. All types of angles can also be found, including rounded, outward, and inward angles. The top surface of the bridges is decorated with circular Côtes de Genève that emanate from the center of the constant-force tourbillon.

The Competitive Landscape

The Grand Seiko Kodo Constant-force Tourbillon is in rarefied company. How often do you see an openworked watch with a co-axial constant-force tourbillon that boasts high finishing? Grand Seiko have made plenty of amazing watches in the past but the Kodo deserves its moment in the spotlight as the crown jewel of the brand and a giant leap for Asian mechanical watchmaking. The watch, limited to 20 pieces only, is priced at USD350,000.

The Kodo might not be a small watch but it is not unwieldy as well. Seiko has done a great job miniaturising the original T0 concept movement to achieve a very wearable case.

Perhaps the most direct alternative to the Grand Seiko Kodo is the IWC Portugieser Constant-Force Tourbillon. Much like the Grand Seiko, the IWC features a tourbillon integrated with constant-force functionality. The constant-force mechanism releases smaller packets of energy every second in a steady manner, ensuring that amplitude remains constant throughout the 48 hours that the mechanism is active (power reserve is 96 hours in total). While the constant-force mechanism is in action, the tourbillon cage rotates in one-second steps; after 48 hours, the constant-force mechanism is disengaged and the cage spins smoothly. The watch also features an ultra-precise moon phase display which only requires a correction once every half a millennium. Compared to the Kodo, the Portugieser is a bigger watch at 46 mm. It also isn’t as well-finished, being mostly machine-finished to meet functional requirements. But at around SGD350,000 (in 2017), the Portugieser is noticeably less expensive than the Kodo and could be considered a value alternative to the latter.

IWC Portugieser Constant-Force Tourbillon

If keeping affairs separate is the preference, then look no further than the Arnold & Son Constant Force Tourbillon. Here, the tourbillon and constant force mechanism are not integrated. The tourbillon cage can be seen rotating smoothly throughout the span of the movement’s 90-hour power reserve. Right next to the tourbillon is the constant force mechanism; like the IWC, a hand is connected to the mechanism to display the jumping seconds. The twin mainspring barrels work in series where only one will unwind at any time. Once the first barrel is nearly depleted, the second one takes over; this smoothens the torque delivered to the gear train. The Arnold& Son is a sizeable 46 mm, so unless you have big wrists, perhaps the Grand Seiko at it’s more manageable 43.8 mm diameter is the way to go. Priced at around the USD200,000 mark, the Arnold & Son Constant Force Tourbillon offers the biggest bang for buck here as long as you are happy to see the two technical complications separate.

Arnold & Son Constant Force Tourbillon

Chief Editor’s note

In addition to the landscape outlined by Frank, I would like to add the Andreas Strehler Trans-axial Remontoir Tourbillon. Aesthetics aside, the Strehler to me is perhaps the closest in terms of features to the Kodo. At least in the spirit of the design goals and approach that uses a remontoir is also mounted co-axially on the axis of the tourbillon. However, there are key differences.

The Kodo’s approach uses a double cage design. The outer cage is driven by the third wheel anchored around the fixed fourth wheel, and provides power to the carriage which is coaxially mounted within this outer cage. The connection between the outer cage and the tourbillon carriage is via the remontoir spring. This technical approach seems to be more integrated in that the tourbillon and remontoir are integrated into a unit, and the entire mechanism rotates around the same axis directly below the tourbillon. Whereas the Trans-axial uses the more conventional method where remontoir mounted on the base plate and drives the tourbillon cage. It does not rotate with the tourbillon cage.

Grand Seiko claims theirs is more efficient, and though we have no way to measure this to affirm or deny, the design does look more elegant with the remontoir and tourbillon being carried in one cage, powered by an outer cage. The Kodo design is much more complex because of this design choice.

Another difference is the frequency of the escapement – the Kodo runs at 28,800 bph, while the Trans-axial at 21,600 bph.

Also, it is interesting to note that the designer of the Kodo is Takuma Kawauchiya who filed he patent for the T0 which was the base for the Kodo. This patent was granted by the Japanese Patent Office in 2014, which is before Strehler’s patent with the Swiss Patent Office granted in 2016. However, Grand Seiko took longer to commercialise the T0 into the Kodo than Strehler who released the Trans-Axial in 2018.

And at a price starting from 182’500CHF (excl. VAT/Tax) with Gold case, the Strehler Trans-axial Remontoir Tourbillon is offered at a much lower price than the Grand Seiko,

Final Thoughts

The Kodo Constant-force Tourbillon is an exciting release from Grand Seiko, not just because of its brooding good looks and technical sophistication, but also the fact that this timepiece is history-in-the-making for the Japanese brand. The watch has broken the Grand Seiko mold, begging the question: is it a one-off, or is the floodgate open for more high-complication mechanical Grand Seiko watches? Whatever the answer is, the Kodo Constant-force Tourbillon is further evidence that Grand Seiko is more than capable of going toe-to-toe with Switzerland’s finest watchmakers.


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  1. Dear Frank, thank you for your story on ‘constant force tourbillons’, however I’m a bit baffled by your statement about Seiko’s (or Grand Seiko of late) quote; ‘or is the floodgate (finally?) open for more high-complication mechanical Grand Seiko watches?’ Come again? Isn’t Grand Seiko, and Seiko historically speaking, a grandmaster of technical innovation and horological firsts throughout watch history? Isn’t the Springdrive thé most innovative step seen in the last 50 years in the watchmaking world? A perfect combination of a mechanical watch with a quartz hart and a complete fluid sweeping hand. No batteries and a five to eight day power reserve because of regenerative breaking! Have you ever seen the Grand Seiko Springdrive chronograph GMT movement through it’s sapphire glass case back? More than 300 parts in that beautiful movement. Or maybe dive a bit back in history to witness the awesome Superior 9983 quartz caliber with a 5 sec deviation, per year! I even believe that it eventually would become the perfect 9F GS movement. Ok I’m missing a step or two but believe me that 9 in 9F is pointing towards a certain caliber made in the end of the seventies. A time when the Swiss where being pummelled by Japanese high end quartz watches outperforming all major Swiss watch brands. Don’t be fooled by Swiss rhetoric that these watches where cheaply made, ’flooded the market’ therefore putting the Swiss out of business. 1. They weren’t cheap at all in the beginning. They where actually quite expensive and 2 they were quite advanced with watchmaker servicable movements sporting multiple jewels, even the cheaper ones. The 7A28 first quartz analog chronograph so well made it was used by the British RAF. Not something to sneeze at. I could go on but please do some research and you will find some landmark innovations made by (Grand) Seiko, a thoroughbred manufacture and worthy to be amongst the highest watchmaker brands. Just saying 😉

    • Thanks Dave. I believe Frank is referring to traditional complications like perpetual calendars, split seconds chronographs, astronomical complications and the like. And is a point which I discussed with Akio Naito, CEO of Seiko. I will publish the discussion soon.

  2. As impressive as it obviously is, and appreciating the strive for chronometric precision—the purpose of watchmaking—having read all articles about it, no article mentions the actual precision rates… and with the latest Spirate from Omega with accuracy of 0/2s, it all seems an exercise in futility… not to mention Tourbillon being useless anyway…

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