Watches & Wonders 2025: Zenith Introduces The GFJ Caliber 135, An Old School Champion Of Precision
The Zenith caliber 135 is one of the most famous high precision movements in the history of watchmaking. Now Zenith has this observatory competition caliber back in production.
The Zenith caliber 135 is not, overall, an especially rare movement, with some 11,000 having been produced between 1949 and 1962, but it has a remarkable track record for precision. The 135 was made in two versions – a commercial model, and one, the 135-O, made specifically for the observatory competitions. The 135-O received a staggering 235 prizes for chronometry over the course of its production, and, in one of the most spectacular winning streaks in the history of watchmaking, five first prizes five times in a row at the Neuchâtel Observatory, from 1950 to 1954.
In 2022, ten vintage 135-O movements were refurbished, finished, and cased as a ten piece limited edition in collaboration with Kari Voutilainen and Phillips; the Zenith Caliber 135 Observatoire Limited Edition was a remarkable accomplishment but it also made the desire of chronometry enthusiasts for a modern production run of the 135 even stronger.
At Watches & Wonders 2025, Zenith has done just that with the GFJ, named for Georges-Favre Jacot, who founded Zenith in 1865, and which houses the Zenith caliber 135, but with some updates to give it features in line with expectations of a modern watch movement.
Externally, this is a richly luxurious watch. The case is in platinum, 39mm in diameter, with elegantly stepped lugs and bezel, and the dial has a central disk of lapis lazuli with tiny golden flakes of pyrite, over a seconds subdial made of mother of pearl. The outer minute track is decorated with a CNC engraved “brick”pattern, inspired by the brick façade of the Zenith factory in Le Locle, and the minute track is decorated with applied white gold beads, and faceted white gold hour markers.
The color blue is sort of a signature color for Zenith – Georges-Favret Jacot’s name for the company, and its star logo, represent the highest point of the heavens as seen at night.
While the dial side of the watch glows with nocturnal radiance, the view through the display back is of both physical and mechanical beauty in equal measure.
The fundamental architecture of the caliber 135 was created by its constructor, watchmaker Ephrim Jobin, for one overarching purpose: the greatest possible precision under the testing regimens established at the Neuchâtel Observatory. The category for wristwatches specified a 13 ligne diameter, which is just under 30mm. Within that space, two of the basic goals were to have as large a balance as possible, and as large a mainspring barrel as practical. A larger mainspring would provide better isochronism (the ability of the oscillator system to beat at a stable frequency regardless of fluctuations in amplitude), and a larger diameter balance would provide a higher moment of inertia. Moment of inertia is the rotational equivalent of linear inertia, which you can think of as resistance to changes in motion caused by external disturbances. Moment of inertia is a function of the radius of the balance and its mass, and a larger balance offers both more mass and a larger radius. (Today, most watch movements use smaller balances, but beating at faster rates – the modern industry standard is 28,800 vph – to achieve the same result, albeit without the stately dignity of a 2.5 Hz frequency).
Normally, the maximum possible diameter of the balance in a hand-wound movement is determined by the diameter of the movement overall, and the placement of the center wheel. The center wheel is the first gear in the going train; it’s turned by the rotation of the mainspring barrel and it rotates once per hour. The pivot of the center wheel runs through the center of the movement, and drives the minute hand (the hour hand is driven off the motion works, which are gears that step down the once-per-hour rotation of the minute hand to once per 24 hours).
In a 13 ligne/30mm movement laid out in this traditional fashion, the diameter of the balance is limited by the position of the center wheel. The only way to increase the balance diameter, if you want greater moment of inertia out of the balance, would be to somehow move the center wheel out of the center of the movement.
In the Zenith 135, you will if you look closely see that there seems to be an extra jewel in the going train. There should be only three train wheel jewels, not counted the escape wheel; center wheel, third wheel, and fourth wheel, which rotates once per minute, and whose pivot extends to the dial side of the movement to drive the seconds hand. In the 135, the “center” wheel, which is also sometimes called the great wheel, is set to the left of a large jewel and pivot at the center of the movement; the great wheel drives the third and fourth wheels. What’s that pivot at the center of the movement?
To get the maximum diameter possible out of the balance, Ephrim Jobin hit on the idea of moving the center wheel to the side, and driving the minute hand indirectly. The center wheel drives the third wheel, but it also drives an additional pinion for the minute hand, the smaller diameter of which, relative to the non-center center wheel, allows the balance to have a larger diameter, and thus, a higher moment of inertia. You might think the gain would be small but when you are competing for an advantage of fractions of a second in a competition that takes weeks, small gains add up. This arrangement also allows for a larger mainspring barrel.
Another break with normal movement architecture is in the position of the escape wheel bridge. Normally, this is on the same level as the barrel, center wheel, and third and fourth wheel bridges. In the 135, the escape wheel bridge is below the level of the other bridges and the rim of the balance passes over it.
The balance spring is a Breguet overcoil type, and the caliber 135 as reintroduced by Zenith has undergone some technical updates – the balance is slightly less heavy than the bimetallic Guillaume balance used in the 135-O, and that, along with reduction in friction along the going train (partly thanks to the use of a modern gear tooth profile) gives the new version of caliber 135 a power reserve of 72 hours. The new version of the caliber 135 uses the double index “fork tailed” regulator sweep found in some of the original cal. 135 movements, and like its predecessor, the new 135 is highly precise at ±2 seconds per day maximum deviation in rate (certified by the COSC).
In a very real sense, the caliber 135 is built around the oscillator; the entire construction of the movement is oriented towards using the largest possible balance for the greatest possible precision. Movements 13 lignes/30mm in diameter (and 5mm thick) were the largest movements allowed in the wristwatch category; any bigger than that, and you would have to enter the movement in the pocket watch category, and generally pocket watches had better precision thanks to their larger balances and more powerful mainsprings.
What Zenith and Ephrim Jobin did, essentially, was to figure out how to reconfigure a traditional watch going train so as to be able to use a pocket watch sized balance in a wristwatch. The value of this strategy is born out by the success of caliber 135 at Neuchâtel; a win in the extremely close competitions in one year might have been a matter of luck to a certain degree, but a five year run shows just how effective Jobin’s design turned out to be (credit also has to be given to the two watchmakers responsible for adjusting and regulating the 135-O for competition – Charles Fleck and René Gygax).
The new caliber 135 is beautifully decorated (the movement bridges are decorated with the same brick motif found on the dial) – much more so than the 135-O, which has the unsentimental, almost Brutalist purposefulness of a midcentury Grand Prix car. But the old saying that beauty is more than skin deep, really applies here. Owning a modern 135 is a link to an era when every effort was being made to obtain the last millisecond advantage in precision possible, and the ingenuity of the caliber 135’s design reflects the single minded pursuit of victory in some of the most demanding and unforgiving competitions in the history of watchmaking.
The Zenith GFA “Georges-Favre Jacot,” case, platinum, 39.15mm x 10.5mm, sapphire crystals front and back, water resistance 50 meters. Dial, lapis lazuli and mother-of-pearl. Movement, Zenith caliber 135, balance diameter 14mm, Breguet overcoil balance spring with fork-tail double index regulator sweep, adjusted to ±2 seconds per day maximum deviation in rate, certified by the COSC. Price, $49,900; seven row “brick” motif bracelet available as an option at purchase.
The 1916 Company is proud to be an authorized retailer for Zenith.