The Zenith El Primero automatic chronograph movement is a worthy contender for the pantheon of the most important mechanical calibres ever manufactured.

With a high beat rate, quickset date mechanism, and full-body winding rotor, these movements are robust, reliable, and accurate - and have  powered everything from the iconic A386 chronograph to the Rolex Daytona and a bevy of lesser known models from brands such as Movado and Waldan. 

In 1996, Zenith one-upped themselves by adding a Flyback feature to their Rainbow line of chronographs (allegedly to be considered for a French Air Force contract that never came to pass), and the watch you see here was born. 

Pressing the reset button after the chronograph is activated results in an instantaneous reset - or 'flyback' - action, allowing for the types precise timing useful to fighter pilots or while waiting at the checkout counter of your local deli.

Unlike the more colorful variant from which the Rainbow collection name was born, this particular example is very much a stark black and white military style, with a crisp, legible dial with printed Tritium Arabic indices, black date wheel at 4:30, and a large luminous handset. A bi-directionally rotating 60-minute timing bezel surrounds its sapphire crystal, featuring oversized ridges for easy grip, and it comes fitted to a multi-link stainless bracelet with signed deployant clasp.

This timepiece dates to the late 1990s and remains in strong condition throughout. It is also accompanied by its inner and outer box set, books, blank warranty card, hangtag, as well as extra links and a spare bezel insert. 

With rugged good looks, an interesting history, and a world-class movement, this piece offers a whole lot for under $5K.

Don't sleep on it!