Watches & Wonders 2026: Zenith Launches Two New Versions Of The GFJ Caliber 135

One of the most famous observatory chronometers of all time was made by Zenith, and its record for precision timekeeping is impressive even today. One of its flagship movements, the caliber 135, was produced between 1949 and 1962 and it was made in two versions – the standard caliber 135, and the 135-O (O for Observatory) made for the observatory time trials. The performance of cal. 135-O seems impossible, but these are the facts: the caliber 135-O took home 235 prizes for chronometry over the course of its production and in the small circle of precision watchmaking fans who revere the observatory competition movements, and the regleurs who sometimes spent weeks bringing them to time, it’s a movement of enormous interest and even romance. So, when Zenith announced the GFJ Caliber 135 last year, it generated enormous excitement, with the only reservations expressed having to do with specifics of the execution. Caliber 135-O on this view, should be treated as a thoroughbred performance machine, not a luxury watch per se, although last year’s launch model was pretty convincing in person (and I thought it was irresistible on the optional platinum bracelet, personally).

The launch version of the caliber was decorated with a pattern of rectangular engravings intended to evoke the bricks of Zenith’s factory in Switzerland, but this year, in two new models, we have a more classic finish that perhaps builds a bit more connective tissue between the original 135-O and the new models. The new GFJ Caliber 135 watches are still clearly examples of refined luxury watchmaking, but the color palette is a bit more restrained than the signature deep blues of the dial on last year’s model. As with last year’s model, the two new ones are both chronometer certified by the COSC.

One of the two new models is in a 39.15mm x 10.5mm tantalum case, with an onyx dial set with trapeze cut diamond indexes, and with a mother of pearl small seconds dial. This is a limited edition of 20 pieces. The other is in yellow gold, and in the same 39.15mm x 10.5mm case dimensions (and the same water resistance: 50 meters). This is a limited edition as well, of 161 pieces.

Bloodstone is a type of chalcedony quartz with red iron oxide inclusions, and although it’s a decorative material by definition (and one much favored as a semiprecious stone, thanks to its hardness and durability) it has a subdued richness which feels very appropriate here. The combination of tantalum and onyx likewise gives a more classic and even slightly technical feel compared to the launch model from last year (although there’s only so technical you’re going to get with diamonds and mother of pearl).

As a material, tantalum is certainly the more technically challenging of the two – it shares some of the machining challenges of platinum in that it tends to stick to and dull cutting tools, as well as being very hard, and its low thermal conductivity means you have to be extra careful to keep the working surfaces well lubricated (one of tantalum’s properties, which I would imagine can make a machinist’s life exciting, is that tantalum dust can ignite spontaneously with air). Its heaviness and hardness are features it shares with its next neighbor over on the periodic table – tungsten – and it has an eerie, blue-grey luster. Along with its hardness, the fact that it is chemically inert and hypoallergenic makes it a good material for watch cases, if you can put up with the machining challenges.

Above is the first version of the caliber 135 launched last year. It’s almost identical to the original but with one major technical update: the balance spring is now a modern Nivarox type alloy and the (large) balance  is now Glucydur (the standard modern balance material) while in the original, we had a blued carbon steel balance spring with a Guillaume-type bimetallic balance. The original balance and spring combination provides very fine control to the regleur for temperature compensation, although it’s not practical in a modern watch thanks to the ease with which carbon steel becomes magnetized (although if it were up to me, I’d do a version of this watch with the original balance and spring and just ship it with a Witschi timing machine and a demagnetizer).

The new limited editions feature a movement with much more traditional finishing:

… which I think a lot of enthusiasts are going to prefer, albeit last year’s version did have a great sense of occasion. One of the interesting features of this movement, is the fact that the center wheel is not actually at the center of the movement. This was part of movement constructor Ephraim Jobin’s original design and the reason is that it gives you room for a larger balance, which means better angular momentum, which means better rate stability. On the dial side, in the lower picture, you can see the (gold colored) driving gear for the indirect minutes, geared to the cannon pinion, on whose post the minute hand is attached. Because the minutes hand is indirectly driven, there is an anti-flutter tension spring on its pivot; similar springs serving a similar purpose can be found in chronograph center seconds hands, as well as in watches with indirectly driven center seconds.

While some of us will only really be satisfied by an uncompromisingly austere, steel cased, plain dial version of this watch, I think the two new limited editions are convincing in their own right – the bloodstone dial is the one I think I gravitate towards, but for both of these watches, the choice of dial materials, dial executions, and case materials gives them a lively play of light, which actually brings out and underscores the beauty of the movement – like taking a high performance athlete and putting them in haute couture.

The Zenith GFJ (Georges Favré Jacot) Caliber 135 limited editions: cases, 39.15mm x 10.5mm, 47.75mm lug to lug; 30M water resistant, in tantalum (20 pieces) or yellow gold (161 pieces). Movement, Zenith caliber 135, hand wound, large diameter balance with overcoil balance spring, running at 18,000 vph/2.5 Hz in 22 jewels; “fork tail” fine regulator index; offset center wheel with indirect drive center minutes. Chronometer certified by the COSC. Prices, in gold, $51,900; in tantalum, $83,400.

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