THE BOTTOM PLATE

Details of the calendar and moon switching functions provide a suggestion of the care exhibited
in the construction and finish of this caliber.

THE ESCAPEMENT

Beating at 36,000 beats per hour, the escapement uses a smooth,
three-spoked Glucydur balance and Nivarox I spring.  Shock protection is provided by high-grade KIF units.  Fine regulation is accomplished with an eccentric screw on the balance cock.  The
regulator and balance spring stud appear to be a proprietary Zenith design and are among the very few slightly “rough” components in the movement.

CONCLUSIONS

By today’s standards the caliber 410 breaks little new
technological ground.  The very fast beat escapement may provide some very slight advantage in running regularity compared to a slower movement of similar quality.  With regard to chronograph
functions, the high beat provides finer resolution (ten beats per second), but no greater accuracy than a slower caliber because of unavoidably imprecise operation of the pushers.

What is absolutely
remarkable about the caliber 410 is the value it provides in today’s high-grade watch market.  Surpassed only by the Piguet and the Lemania 2300 series chronographs, the 410 is available at
significantly lower cost.  The El Primero’s craftsmanship falls short of both, and it is functionally somewhat  inferior to the technically more sophisticated Piguets.  But it is, in its own
right, a well-made, well-crafted, honest piece of work that functions well and defines an entire class of midrange chronographs in which it is the sole entry.  In addition to the line of Zenith watches
in which it is available, the El Primero is available from a handful of other manufacturers, including Rolex, and affords the opportunity to own a contemporary Rolex with a relatively high-grade
movement.