For much of its modern history, Zenith has been almost inseparable from the El Primero. Yet long before the arrival of its famous automatic chronograph in 1969, the manufacture had established an equally important reputation for precision timekeeping. At the centre of this was the Calibre 135, a movement developed specifically for the observatory chronometer competitions of the mid-20th century and one that would become among the most celebrated movements in Zenith's history.
Introduced in 1948 and designed by Ephrem Jobin, the Calibre 135 was built around the pursuit of chronometric performance. Its unusual architecture positioned the gear train off-centre, creating enough space for an enormous 14mm balance wheel within a movement measuring just 30mm across. Beating at a relatively slow 18,000 vibrations per hour and paired with a Breguet overcoil, this oversized balance provided the stability required for the demanding observatory trials.
The results were remarkable. Between 1950 and 1954, Zenith achieved five consecutive first prizes in the wristwatch category at the Neuchâtel Observatory, while the competition-specification 135-O would ultimately receive more than 230 chronometry prizes. Around 11,000 examples of the Calibre 135 were produced between 1949 and 1962, though only a small proportion were the specially prepared movements intended for observatory competition.
In 2022, Zenith revisited this history with a series of just ten watches using original vintage 135-O movements that had never previously been cased. These were restored and finished in collaboration with Kari Voutilainen, introducing the Calibre 135 to an entirely new generation of collectors. Three years later, for its 160th anniversary in 2025, Zenith went considerably further with the G.F.J., named after the manufacture's founder, Georges Favre-Jacot. Rather than simply restoring another group of vintage movements, Zenith placed the Calibre 135 back into production for the first time in more than six decades.
The new Calibre 135 remains remarkably faithful to the architecture of the original. The distinctive bridge layout, oversized balance wheel, Breguet overcoil and slow 18,000 vibrations per hour frequency have all been retained, while the movement itself has been extensively re-engineered for modern use. Power reserve has almost doubled to 72 hours, shock protection has been added and a stop-seconds mechanism allows for precise setting. More importantly, each movement is COSC certified and individually adjusted by Zenith to an accuracy of +/- 2 seconds per day, preserving the chronometric purpose for which the 135 was originally created.
The movement is also finished to a level rarely associated with modern Zenith. Its bridges feature a distinctive brick guilloché pattern inspired by the red and white brick facade of the manufacture in Le Locle, complemented by hand-finished bevels and inward angles. It is an interesting balance between the industrial character of the original 135 and the considerably more elevated finishing expected from a modern watch at this level.
The same brick motif continues onto the dial, which is perhaps the most visually distinctive aspect of the G.F.J. A dark blue guilloché chapter ring surrounds a central disc of natural lapis lazuli, its deep blue surface punctuated by naturally occurring pyrite inclusions. At 6 o'clock, the oversized subsidiary seconds is formed from blue mother-of-pearl, introducing yet another texture and shade of blue. Faceted white gold hour markers and hands sit above the dial, while a small pearl-style minute track provides a subtle reference to vintage chronometer dials.
Despite the amount of detail, the watch itself remains relatively restrained in proportion. The platinum case measures 39.15mm across and approximately 10.5mm thick, with a stepped bezel, box-shaped sapphire crystal and sharply defined lugs. These dimensions, together with the simple time-only layout, allow the G.F.J. to retain much of the character of the mid-century chronometers that inspired it rather than feeling like an oversized modern reinterpretation.
Limited to 160 pieces for Zenith's 160th anniversary, the G.F.J. is significant for reasons that extend considerably beyond the anniversary itself. For decades, the El Primero has understandably dominated the way collectors view Zenith, while the manufacture's extraordinary history in observatory chronometry has remained comparatively overlooked. The G.F.J. changes this by returning one of Zenith's most important movements to serial production, while retaining the unusual architecture and slow-beating oversized balance that made the original so successful.
For me, this is what makes the G.F.J. particularly interesting. It is not simply a modern watch inspired by something from Zenith's archives, but the genuine revival of a movement architecture that helped establish the manufacture's reputation for precision more than 75 years ago. Combined here with the platinum case, lapis lazuli and mother-of-pearl dial, it also feels appropriately special for the first production watch to mark the return of the Calibre 135.
