Zenith Caliber 135 Port Royale Chronometre, 36.1 mm Steel, Ultra-Rare Circa 1960

Zenith Caliber 135 Port Royale Chronometre, 36.1 mm Steel, Ultra-Rare Circa 1960

Zenith introduced Caliber 135 in 1948 to enter it into observatory competitions. The Caliber won numerous prestigious awards and prizes, including an unprecedented five consecutive Neuchâtel Observatory chronometry prizes from 1950 to 1954. In all, the movement earned 200 honors, two-thirds of which were first prizes. To this day, Caliber 135 remains a legend in Swiss watchmaking.

The watch features an original and untouched two-tome silver dial. The Zenith star logo and hour markers are applied.

The condition of this watch is remarkable. Case is without a doubt unpolished, the dial is perfect and original, and the case back is free of scratches with clear serial number visible. There is a small hallmark on the front of the top left lug which is characteristic of watches imported to the Portuguese market.

The Caliber

The design innovations of Cal 135 included a large barrel for improved isochronism and power reserve, as well as an oversized balance which, as part of the regulating organ, plays a crucial role in enhancing precision. In this model, the larger balance generates a higher rotational inertia that allows more consistent performance, without increasing weight or beat rate. Zenith also offset the minute wheel from the central axis so as to provide space for the enlarged balance. The observatory competition version of Caliber 135.0 was equipped with a Breguet overcoil balance-spring, as well as a single or double arrow-shaped index or regulator ensuring balanced friction and enabling optimal adjustment.

The size of the movement was pushed to 30mm (13”) which is the maximum size a watch can be for the Neuchâtel Observatory competition before getting placed into the pocket watch category. The Cal 135 beats at 18,000 vph, features 19 jewels and has a slim movement, at 5mm.

Owing to the exacting nature of producing a chronometer-grade watch, only 11,000 examples of Cal 135 were produced from 1949-1962.

Dial: Original, Two-Tone Silver

Case: Stainless Steel, snap back, serial number: 9483912

Dimension: 36 mm diameter, 10 mm thick.

Movement: Zenith Chronometer Grade Cal 135.

Winding: Manual

Frequency: 18,000 vph

Jewels: 19

Signatures; Dial, Case, Movement