Zenith El Primero: A Comprehensive Guide to the Historic Chronograph Caliber

The Zenith El Primero, found today in watches throughout Zenith’s collection, from the Chronomaster to the Defy to the Pilot, is arguably the watch world’s most famous movement — more widely known, in fact, than some of the watch models to whom it has given life during its half-century-plus of existence. The reasons for its renown are several, from the technical revolution it represented at its origin to the legendary role it played in the post-Quartz Crisis revival of the mechanical watch. Here we examine what made the El Primero so special in the first place and introduce you to some modern watches that demonstrate how it is still evolving and improving in the 21st century.

A FOUNDATION OF PRECISION

Watchmaker Georges Favre-Jacot was a mere 22 years of age when he founded the atelier that would become Zenith in Le Locle, Switzerland in 1865. Favre-Jacot, a contemporary of Swiss modern architecture pioneer le Corbusier, took his own pioneering approach to making watches, becoming one of the first to bring the various horological disciplines under one roof as opposed to the more common établissage system that most watchmakers used at the time, which had different parts made in different small workshops before being delivered to another workshop for assembly into a finished watch, Georges Favre-Jacot & co. became Zenith in 1911, the company taking its new name from a top-of-the-line movement it created that won a Grand Prix for precision at the 1900 Paris World’s Fair. Another of the company’s historical movements, Caliber 135, dominated the Neuchâtel Observatory’s chronometry awards for an unprecedented five years, from 1950 to 1954. In all, Zenith would go on to win 2,330 chronometry prizes over the years — a record that still stands — establishing the brand as a leader in the pursuit of timekeeping precision.

A CHRONOGRAPH REVOLUTION

It was in that spirit that Zenith, on the occasion of its 100th anniversary in 1965, decided to tackle the biggest technical challenge that faced the watch industry to that point: the invention of a self-winding mechanical chronograph movement. Self-winding, or automatic, watch calibers had been around in some form since Abraham-Louis Perrelet invented the first one in 1770, but the technology had yet to be successfully applied to a chronograph caliber. Zenith missed its self-imposed deadline to complete the project in its centennial year, and other watch manufacturers began throwing their hat in the ring subsequently, all vying to be the first to lay claim to the first great horological invention of the 20th century.

During the next few years, the Great Automatic Chronograph Race kicked into high gear, with Zenith competing against a consortium of Swiss firms that had teamed up to develop its own self-winding chronograph caliber (made up of Heuer-Leonidas, Breitling, Buren-Hamilton, and Dubois-Depraz), as well as Japan’s Seiko, which like Zenith was pursuing the project on its own. Zenith’s movement made it to the finish line first, announced at a press conference on January 10, 1969 — beating the Caliber 11 “Chrono-Matic” that arose from the Breitling-Heuer consortium’s efforts, which launched on March 10 of that year, and the Seiko Caliber 6139, which hit the market in May. While Zenith’s groundbreaking movement was not actually available in a commercial product until later in the year, it did live up to the name its creators gave it — “El Primero,” or “The First” — by virtue of its January debut to the public.

In keeping with Zenith’s historical mission statement of pushing the boundaries of timekeeping accuracy, the original El Primero (Caliber 3019H) was “the first” in many regards. In addition to its self-winding properties, Despite the complexity endowed by its 278 parts, it measured just 6.5 mm in height, meaning watches that contained it could be similarly slim and wearable. Its all-new dry lubricant based on molybdenum sulfate helped ensure long-term precision by lessening friction. Its balance frequency was an unprecedented, lightning-quick 36,600 vph (5 Hz), which in practical terms meant that the built-in stopwatch function, driven by a classical column wheel, was capable of measuring elapsed times to 1/10th second — a significant achievement considering that most chronograph calibers to that point oscillated at 21,600 vph (as Seiko’s caliber did) or 19,600 (like the Chrono-Matic); even today, 28,800 vph, or 4 Hz, is the standard for most chronograph movements.The rotor that wound the movement had a tungsten carbide weight that maximized each motion of the watch’s wearer’s arm to continually wind the mainspring. The El Primero’s power reserve was nearly 50 hours, well above the standard at the time.

THE FIRST OF THE FIRST

The first Zenith watches equipped with the El Primero caliber hit retailers’ shelves in September 1969. The first of these models was the Ref. 384, which had a 37mm stainless steel tonneau case with mushroom-style pushers, and a tricompax dial with three black subdials on a silvery white background (a style today widely known as a “panda” dial), a red central chronograph hand, and a tachymeter scale on its periphery. Following up that model and employing the same case design was Ref. A385, which sported, according to Zenith, the watch industry’s first gradient-effect “smoked” dial, cream-colored in the center radiating to brown and blalck at the edges, along with silvered white subdials. The model that would prove most durable and influential was Ref. A386, which established the tricolor design that has become visual shorthand for a Zenith El Primero watch to this day: blue for the minute counter at 3 o’clock, gray for the hours counter at 6 o’clock, and silver for the running seconds at 9 o’clock. These seminal designs, resurrected as the Chronomaster Original series, remain a tentpole of Zenith’s collection, one of several distinctive subfamilies under the Chronomaster banner.

TREASURE IN THE ATTIC

In s somewhat ironic coda to the origin story of the El Primero and its pioneering automatic chronograph brethren in 1969, that same year saw the birth of another major innovation in the world of watchmaking, one that would profoundly impact the future of the industry for decades to come: the development of quartz movements. Drawing their energy from electronic batteries rather than traditional mechanical escapements, watches that were outfitted with these movements could be mass produced at a fraction of the cost of a mechanical watch. It was the Japanese — led by Seiko, which made the first quartz wristwatch, the Astron — that first took up the gauntlet of producing the bulk of these more accessible timepieces, while the Swiss, more inclined to stick to centuries-old tradition, were slow to adopt the new invention. Zenith was no exception. By 1971, the watchmaker had been gobbled up by another company named Zenith, which made TV sets and radios and thus, not surprisingly, regarded electronic timekeeping as the wave of the future. The corporate edict went out to the team in Switzerland in 1975, not only to terminate mechanical watchmaking and gear up for an all-quartz future but also to destroy all the existing parts and blueprints for Zenith’s mechanical calibers. 

This turn of events would very likely have been the death knell for El Primero, just a few years after it had made its debut, but for the determination, and quiet insubordination, of one man, a senior engineer in Zenith’s movement-making department named Charles Vermot (above). Enlisting the aid of a handful of co-workers, Vermot secretly stashed all the El Primero blueprints and parts in a hidden attic at the factory (now preserved for posterity, see below) in the hopes of waiting out the turbulent era that would become known as the Quartz Crisis and one day being able to resume production of the groundbreaking chronograph caliber. The clandestine mission is now the stuff of watchmaking legend; Vermot’s son once told me that his father had to devote so much after-hours time to it that his mother was convinced Charles was having an affair. Ultimately, Vermot’s instincts proved correct, his initiative bore fruit, and his defiance was rewarded: rumors of the mechanical luxury watch’s death proved greatly exaggerated and when Zenith began its next chapter under the ownership of the LVMH (Louis Vuitton Moêt Hennessy) luxury group in 1999, the El Primero was poised to reclaim its central role in Zenith’s collection.

BEHIND THE SCENES

Whereas the El Primero is rightly regarded as Zenith’s most important contribution to horological history, the high-frequency movement has had an impact on some other brands as well. In fact, the catalyst for the El Primero’s emergence from its corporate-mandated hibernation came from an unexpected and highly prestigious source: watch-industry 800-pound gorilla Rolex, which reached out to Zenith in 1998 in search of a new self-winding chronograph caliber for its red-hot sport-luxury watch, the Cosmograph Daytona. (Believe it or not, the Daytona was still using a manually wound movement at that point.) Vermot’s timely revelation that he had secretly hoarded all the necessary elements to mass-produce El Primero calibers built to Rolex’s specifications was the shot in the arm the struggling watchmaker needed to begin rebuilding its brand equity as the mechanical watch renaissance began to ramp up. The modified movement, which Rolex named Caliber 4030, had the date function removed and was adjusted for a slower frequency of 28,800 vph. This generation of “Zenith” Daytonas, now extremely collectible on the secondary market, continued right through the turn of the millennium, in 2000, when Rolex finally installed its own in-house chronograph calibers in the Daytona.

And while the Rolex Daytona is by far the most famous watch to house the Zenith El Primero, it is not the only one. The high-frequency caliber’s legendary attributes have made it an ideal choice for other manufacturers in need of a sturdy, reliable, precise chronograph engine over the years, most but not all of them Zenith’s sister brands within LVMH. The El Primero is the base for TAG Heuer’s Caliber 36, found in select models from the Carrera and Monaco families. Hublot’s automatic HUB 4700, found in its tonneau-cased Spirit of Big Bang series, is a skeletonized version of the El Primero Caliber 400. Even LVMH stablemate Bulgari, prolific maker of record-breaking ultra-thin complicated calibers, uses the El Primero as the base for the BVL 328 movement inside its Octo Velocissimo Chronograph. Outside LVMH, El Primero served as the foundation of Panerai’s OP IV and OP VI chronograph movements. And if its starring role in the Rolex Daytona didn’t earn the El Primero enough ‘80s cred, its use in the Ebel 1911 Chronograph of that era — famously, the watch worn by Don Johnson as Detective Sonny Crockett on Miami Vice — certainly should.

NEW MILLENNIUM, NEW FRONTIERS

With El Primero firmly entrenched as its flagship in-house movement, Zenith has introduced numerous variations on it over the years. The manufacture’s other home-grown movement series, the Elite, is essentially an El Primero with the chronograph function stripped out; this three-hand caliber animates a family of watches also named Elite, as well as many of the Pilot Type 20 models. A skeletonized variant of the Elite powers many models in the Defy Classic series. Zenith has developed El Primero calibers with flyback functions, big dates, power reserve indicators, moon-phases, annual calendars, and even tourbillons. But the boldest update to the El Primero was the one that managed to incrementally improve upon one of its core technical attributes: its rarely matched 36,600-vph frequency. The 9004 caliber inside 2017’s Defy El Primero 21 did exactly that, equipped with two separate escapements and an integrated chronograph function that measures stopped times not just to the El Primero’s standard 1/10-second interval but to a nearly unprecedented 1/100th second. One escapement beats at a lightning-quick 50 Hz (360,000 vph), sending the chronograph’s central seconds hand speeding around the dial once per second, while the other escapement beats at 36,000 vph, or 5 Hz, to regulates the hours, minutes, and running seconds. In addition to the two escapements, the movement has two mainspring barrels to maintain separate power reserves for the timekeeping (60 hours) and the chronograph (50 hours). The movement’s balance spring is made of carbon-matrix carbon nanotube composite, a Zenith-patented material that is resistant to gravity and temperature fluctuations and anti-magnetic to 15,000 gauss; it’s also COSC-certified for chronomnetric precision, and installed inside a 44mm case made of titanium or ceramized aluminum. This ultra-high-frequency descendant of the El Primero continues to find a home inside select models within the avant-garde Defy series, including a Double Tourbillon model introduced in the El Primero’s 50th anniversary year of 2019.

CELEBRATING HALF A CENTURY

Speaking of that milestone anniversary year, Zenith pulled out all the stops in 2019 both to pay homage to the El Primero's origins and to revamp it for the future. Leading the semicentennial tribute pieces was a revival of the Ref. A386, largely faithful to the vintage piece and just a smidgen larger in diameter (38mm), equipped with El Primero Caliber 400 and hosting the familiar case shape and tricolor dial of its ancestor. Aside from the extra millimeter of size, the case’s only significant modern modification was the sapphire exhibition caseback to showcase the movement. Perhaps not surprisingly in our current era of vintage-mania, this limited-edition piece was popular enough to kick off an entire family of Chronomaster Revival models, comprised not only of contemporary re-editions of classics like the A384, A385, and A386, but also — in the grand tradition of Zenith acquiring ideas from plans and parts stashed away in its factory’s attics — a handful of pieces based on unrealized prototypes like the Manufacture Edition, with its subdials executed in three shades of blue rather than blue-gray-silver, and the black-tinted “Shadow” edition (below), both of which were released in 2020.

Also debuting in 2019 was the technically ambitious but perplexingly named Zenith Defy Inventor, which brought to serial production the Defy Lab prototype series from two years earlier. That model marked the debut of the Zenith oscillator, a single-piece, ultra-thin mechanism made of monocrystalline silicon (as compared to the 30-odd parts in a traditional balance), which oscillates at a breakneck pace of 108,000 vph, or 18 Hz, dwarfing even the 36,600-vph (5 Hz) of the El Primero. The openworked dial is designed to allow a view of the oscillator's pulsations; its benefits include increased reliability — the absence of 30 or more moving parts drastically reducing friction, wear, and deformation — and a higher level of temperature stability and magnetic resistance thanks to the use of silicon. Additionally, the unique construction of the escape wheel, with its flexible blades, enhances precision. There was no chronograph integrated into the Defy Inventor caliber, but the innovative system was clearly a successor to the original El Primero and carried on Zenith’s historical quest for the highest level of timekeeping reliability.

SPEEDIER AND SPORTIER

In 2021, inspired by the limited-edition Chronomaster 2 model from the 50th anniversary set, Zenith introduced the Chronomaster Sport, which is significantly the first regular-production model that wears its exceptional chronograph precision on its face as a badge of honor. The watch’s polished ceramic bezels (used here for the first time on a Chronmaster) are etched with a graduated 1/10-second scale that enables reading of the time to this fraction of a second. Powered by the most recently updated version of the El Primero, the watch’s central chronograph seconds hand makes a complete rotation around the dial in 10 seconds rather than the usual 60, enabling 1/10-second readings directly on the bezel when the hand is stopped. The movement’s other upgrades, which are displayed behind a sapphire caseback, include an enlarged blue column wheel, a lever-operated lateral clutch, and an openworked rotor with a Zenith star emblem. It also features a stop-seconds function, an extended power reserve of  60 hours (10 hours more than the standard El Primero’s 50 hours) and an improved teeth design for the wheels for more precise timing.And while the Chronomaster Sport is decidedly contemporary in its technology and design, many of its elements hearken back to the classic Ref. A386 from 1969, including the pump-style pushers on the 41mm steel case and the blue-gray-silver overlapping chronograph subdials and 4:30 date window.

The other major launch for Zenith in 2021 was the Defy Extreme collection, an ultra-sporty spinoff of the main Defy line with larger cases (45mm diameter, 15.4mm thick), most of them in titanium, integrated, interchangeable bracelets and straps as per current sport-luxury trends; and inside, the skeletonized El Primero Caliber 9004, the groundbreaking 360,000-vph caliber that debuted in the Defy El Primero 21 with dual escapements.

DEFIANTLY DIFFERENT

With the new Defy Skyline, unveiled in early 2022, Zenith reimagines the El Primero’s legendary high-frequency timing performance for a subtler, non-chronograph style of timepiece, while once again paying homage to the company’s history. The octagonal 41mm case in stainless steel is derived from the avant-garde “bank vault” case of the first Defy wristwatch, which debuted alongside the first El Primero models in 1969. Its 12-sided faceted bezel aligns with the hour markers on the dial, which is enhanced with a repeating pattern of four-pointed stars that visually recall a vintage Zenith logo from the ‘60s. Also on the dial, and only subtly noticed at first glance, is a small seconds subdial at 9 o’clock, balancing the date window at 3 o’clock, whose constantly running seconds hand makes a complete revolution every 10 seconds rather than every 60 — a dynamic display courtesy of the 36,600-vph frequency of the re-engineered, sans-chronograph El Primero 3620 caliber.

A GRAND RE-OPENING

The most recent expansion of the El Primero series took place at Watches & Wonders Geneva 2022. In 2003, during what is today mostly regarded as an age of excess for the brand, Zenith introduced the first Chronomaster Open, a chronograph wristwatch with a partially open dial to display the regulating organ of the movement inside. After several years off the market as Zenith re-tooled its collection under new leadership, the Chronomaster Open returned to the lineup, now significantly streamlined from its early-aughts predecessor. The case, in steel or rose gold, measures a relatively modest 39.5 mm in diameter. The dial, in matte silver or matte black, features the now-familiar tricolor three-register layout, with one significant difference: the traditional 9 o’clock subdial, while still retaining its hand to track the running seconds, has been replaced with a hesalite crystal in a carved-out window that allows a view of the star-shaped silicon escape wheel of the movement, El Primero Caliber 3604. Based on the optimized Caliber 3600 installed in recent versions of the Chronomaster Sport and Chronomaster Original, the movement boasts that caliber’s 1/10-second chronograph precision and its lengthy 60-hour power reserve.

More than 50 years after it burst upon the horological scene, and decades after its return from watchmaking limbo, the Zenith El Primero continues to play a relevant role in the ongoing story of both Zenith and the watch industry as a whole. The movement introduced in 1969 may have been “The First” of its kind but, as Zenith’s recent innovative updates to it have demonstrated, it was far from The Last.