For the aforementioned reasons, indirect center seconds was not a satisfactory solution for many manufacturers. In 1948, Zenith released the caliber 133. This "bumper" automatic was a 13''' movement and was, for the time, remarkably thin at 4.9 millimeters.
With the caliber 133, Zenith had finally reorganized the traditional gear train to provide for directly-driven center seconds. The design not only provided a simple and stable center seconds display, it also allowed more room in the movement for both a larger balance and larger mainspring barrel. The performance advantages of this reorganization were significant enough that the design, or variations on it, were to become a standard in the Swiss watch industry.As illustrated above, the fourth wheel is moved to the center of the movement to carry the seconds hand on its extended pinion. The center--or, now, minute--wheel is moved out of the center to drive the cannon pinion (which carries the minute hand) indirectly. Because the fourth wheel is in the power flow (and under load), the seconds display is completely stable. Any instability in the minute hand is masked by its relatively slow travel. An example of directly-driven center seconds with an indirect minute drive may me seen in the Omega Coaxial, based on the popular ETA 2892 (below).
As illustrated above, the fourth wheel is moved to the center of the movement to carry the seconds hand on its extended pinion. The center--or, now, minute--wheel is moved out of the center to drive the cannon pinion (which carries the minute hand) indirectly. Because the fourth wheel is in the power flow (and under load), the seconds display is completely stable. Any instability in the minute hand is masked by its relatively slow travel. An example of directly-driven center seconds with an indirect minute drive may me seen in the Omega Coaxial, based on the popular ETA 2892 (below).
The center (or minute) wheel is indicated at (1), the third wheel at (2), and the fourth wheel at (3). The fourth wheel is in the center of the movement and the sweep seconds hand is carried on the long fourth wheel pinion extending through the plate to the dial side. The center wheel drives the cannon pinion via an intermediate wheel on the bottom plate (not visible). This construction is now extremely common in center seconds designs.
As photographed right, the center wheel (1) and fourth wheel (2) are seen stacked in the center of the movement. A retaining spring for the fourth wheel upper pivot is indicated at (3), the third wheel at (4).
The origins of the SC in Patek's conventional hand-wind calibers can be seen left. The escape wheel (1) lies in a conventional position in the bottom of the movement. The wheel is driven by the fourth wheel (4) by means of an extended pinion (2) and pinion gear (3). Note the "elevation" of the escape wheel cock (5). The entire wheel train bridge is similarly formed (inset).
In so many areas of technology, yesterday's challenge is today's assumption. Like other technologies, the road to contemporary center-seconds designs is filled with interesting waypoints. The two Pateks illustrated here are among them. Unnecessary in the much larger "pocket" watch, center seconds has immensely improved the utility of the wristwatch. It is, as they say, here to stay.
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