Zenith 12 NVSI

Description

This beautiful 11 ​​1/2 ligne caliber, marked “A.E.S.”, is not easy to identify, but it is very likely a Zenith 12 NVSI, built between 1904 and 1926. According to the serial number, this example should have been manufactured between 1911 and 1913.

As can be seen from the gold-colored base plate with its set bearing jewels, this is a high-quality movement. Interestingly, all the jewels on the base plate are transparent, while those on the bridges and cocks, visible from the outside, are ruby-red.

The Zenith 12 NVSI uses a so-called negative setting mechanism, which is located on the base plate. The initial position is the crown pulled out. Here, the clutch pinion engages with the dial-side hand-setting wheel. When the crown is now pushed in and the end of the crown stem moves the lever, a deflection mechanism pushes the clutch pinion outward, thus engaging the Breguet clutch of the winding mechanism.

The gear train design is very classic: Mainspring barrel, central minute wheel, third wheel, decentral seconds wheel at 6 o’clock (hunter-case design, i.e., 90° to the crown stem), and an escape wheel.

The escape wheel is mounted under its own cock; the seconds and third wheels share another cock, and the minute wheel bearing is part of the gear train bridge.

The lever of the Zenith 12 NVSI is of particularly high quality, with all its edges beveled.

The balance section is also very elaborate and well-made, using a bimetallic screw balance that beats at 18,000 A/h.

Attached to it is a hairspring with a curved (Breguet) terminal curve to compensate for positional errors.

The effective length of the hairspring is regulated by a cam disc, supported by a type of swan-neck spring.

The bimetallic design with its slots is intended to compensate for temperature-related changes in the hairspring.

As impressive as the movement is on the movement side, the dial side is very unspectacular; even the balance bearing is covered only by a simple cover plate and capstone. Since the winding mechanism is located on the inside, the dial side is otherwise empty, except for the change wheel.

In the lab

Timegrapher result

Unfortunately, age has taken its toll on the accuracy of the movement; despite the screw balance and fine adjustment, it didn’t match the expected chronometer accuracy. Nevertheless, the rates ​​are quite good for a movement over 100 years old that was robbed of its case (presumably made of gold).
Since the lift angle is unknown, it is likely that the amplitudes were measured too high. The values, measured at the standard 52°, support this suspicion.

Technical data

Usage gallery