Making the World's Most Accurate Watches: A History of Timekeeping Accuracy

Nearly every advance in watchmaking technology has been in the service of increased utility and functionality — even inventions that we now consider entirely luxurious affectations. The minute repeater, for example, was invented so a watch wearer could audibly check the time in the dark in the days before luminous treatment on dials. Even the tourbillon began its existence as a device for enhancing timekeeping accuracy, countering the effects of gravity on a pocketwatch’s movement. Thus it should come as no surprise that as the world entered the electronic era in the mid-20th century, watchmakers would attempt to harness the new technologies to improve the precision — and hence the desirability — of their products. Read on as we trace the evolution of timekeeping technology all the way up through today’s most accurate watches. 

Birth of the Chronometer

Not long after the tracking of time migrated from giant clocks in the town square to portable devices carried in waistcoat pockets, and eventually worn on wrists (click here for a brief history of watches), the need for a standard of dependable accuracy in these mechanical timekeepers became evident. Hence the establishment of standards for which a timepiece could be deemed a "chronometer."

The classical definition of a chronometer goes all the way back to the golden age of seafaring exploration in the 18th Century, when ships required the use of a highly accurate onboard clock that enabled their navigators to determine longitude in order to avoid the perils of running aground or veering hopelessly off course. The man credited with developing the first of these “marine chronometers” was legendary British watchmaker John Harrison; his invention facilitated the celestial navigation used at the time to determine their ship’s position in coordination with a sextant. Marine chronometers (above), which were essentially highly accurate clocks mounted on gimbals inside wooden boxes, were among the first portable timepieces; they were instrumental in the global seagoing trade that helped build our modern, interconnected world. 

The term “chronometer” took on a slightly broader meaning as pocket watches and later wristwatches became widely adopted. Watchmakers focused on the task of optimizing their timepieces’ precision and submitted their proudest accomplishments in the field to “chronometer competitions” — tests conducted at facilities like Switzerland’s Neuchâtel Observatory (above) and London’s Kew Observatory — throughout the late 19th to mid-20th Century. Zenith, with 2,330 chronometry prizes for accuracy, holds the record for the most historical accolades at these Observatory Trials, which were gradually phased out as the quartz watch became ascendant in the 1970s.

The Contrôle officiel suisse des Chronomètres (Official Swiss Chronometer Testing Institute, aka COSC) was founded in 1973 as the organization responsible for testing Swiss-made watches for accuracy and precision in order to certify them as chronometers according to the international ISO 3159 standard. A COSC certification remains the baseline standard for an “official” chronometer watch, many of which still use mechanical movements. The maximum average daily rate deviation for a mechanical movement to obtain a COSC chronometer certificate is -4/+6 seconds; for a quartz movement — which COSC tests for 13 days rather than 15, in only one position and at several different temperatures and humidity levels — the maximum is +/- 0.07 seconds per day. As I explore in more detail here, there are now several standards of chronometer certification for today’s luxury watches, each with their own criteria, some of them even more stringent than COSC’s.

The Great Chronograph Race of ‘69

The quest for new heights of accuracy proved important not only in the area of timekeeping but also in the recording of elapsed time intervals with stopwatches and chronographs, for sporting events like horse racing and automobile racing. In its 100th anniversary year of 1965, Zenith decided to tackle the biggest technical challenge that faced the watch industry to that point: the invention of a self-winding mechanical chronograph movement that would also be a paragon of precision. 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. 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. 

The Zenith El Primero continued to carry the banner of mechanical chronographic precision well into the 21st Century. In 2017, the El Primero 21, aka Caliber 9004, took its ancestor’s 36,000-vph frequency and multiplied it by a factor of 10, making the timepiece that contained it the first mechanical watch able to measure elapsed  times to 1/100 second as well as display them. The central chronograph hand makes a complete rotation around the dial once per second rather than the standard once per minute and points to an ultra-precise 1/100-second measurement on a graduated bezel. Zenith’s Defy Extreme models (above) are among the watches currently equipped with El Primero Caliber 9004. Two years later, for the El Primero’s 50th anniversary, Zenith unveiled the Defy Lab, a prototype whose oscillator was made from a wafer of silicon and served as a single-piece replacement for the movement’s sprung balance (balance wheel, balance spring, and lever) and thus eliminated the need for lubrication while removing the risk of friction. The movement equipped with the oscillator had a frequency of 15 Hz (compared to the 5 Hz of the El Primero) and a daily precision rate of 0.3 seconds, an unprecedented rate for a mechanical movement. The 10 watches outfitted with the regulator sold out swiftly, but Zenith continues to use the historic regulator device in its Defy Inventor models.

Eastern Innovation: Quartz to Eco-Drive

Even as mechanical watches, including chronographs, were becoming more accurate, the emergence of electronics into timekeeping was aimed at making all these advances obsolete. American watchmaker Hamilton led the way with the world’s first electronic watch, the Ventura, which debuted to great fanfare in 1957 and would go on to even greater fame when it was worn by Elvis Presley in the 1961 film, Blue Hawaii. The watch was notable not only for its unusual, futuristic curved case design but for its movement, Caliber 500, which used a battery, magnets, and an electronic coil rather than a mainspring to drive the gear train and balance wheel. The Ventura (above) remains a presence in Hamilton's collection today, though modern models are now equipped with quartz or mechanical movements rather than the now-outdated electronic mechanism.

New York-based Bulova joined the high-tech timekeeping fray in 1960 with the groundbreaking invention of the Accutron Spaceview 214, which took its numerical designation from its movement, Caliber 214. The Accutron technology replaced the balance wheel common to mechanical movements with a tuning fork, powered by a one-transistor electronic oscillator,  to drive the timekeeping functions. This system ensured an oscillation rate of 360 hertz — nearly 150 times faster than that of a mechanical, balance-wheel-driven timepiece — and promised an accuracy to just one minute per month, an unprecedented precision level that inspired the name Accutron, for “Accuracy through Electronic.” In 2020, Accutron spun off from Bulova to become an independent brand, and arrived on the scene with a new electrostatic movement with an accuracy to just +/-5 seconds per month.

However, the true watershed moment for high-tech timekeeping on the wrist didn’t arrive until 1969. While Seiko was unveiling its first automatic chronograph movement, it was simultaneously working to shake up the watch community that same year with the introduction of the Seiko Quartz Astron, equipped with Caliber 35A — the first quartz wristwatch movement. Unlike a mechanical movement, which stores its energy in a wound mainspring inside a barrel and releases it through a complex series of gears to move the hands, a quartz movement derives its power from a small electrical charge provided by a battery, which then passes through an integrated circuit that applies the charge to a tiny quartz crystal shaped like a tuning fork. The incredibly high rate of that crystal’s vibration dwarfs that of a mechanical movement (32,768 times per second, as opposed to the 3 or 4 times per second offered by most mechanical oscillators), and drives the second hand only once per second with the aid of a tiny motor, a development that had never before been seen in watches, conserving energy and ensuring an accuracy of just -/+ 5 seconds per month. 

The Swiss were slower than the Japanese to embrace quartz technology, which led to the so-called “Quartz Crisis” of the 1970s and ‘80s that threatened to wipe out the nation’s steadfastly traditional watch companies. There were exceptions, however, such as Longines, which developed the first quartz clock as early as 1954 and incorporated it into a sports-timing instrument called the Chronocinégines. This device provided racing judges with a series of pictures recorded on film at 1/100th second, allowing them to precisely record the moment an athlete crossed a finish line. In 1984, Longines followed up this innovation with a groundbreaking quartz wristwatch, the Conquest VHP (above). The modern version of that watch debuted in 2017, equipped with the ETA-manufactured Caliber L288.2, which boasts an exceptionally high degree of precision for an analog watch (± 5 seconds per year) and an innovative GPD (gear position detection) system that quickly resets the watch’s hands after an impact or exposure to a magnetic field. The movement also features an extra-long battery life of almost five years — better than a smartwatch, which requires constant battery recharges — and a built-in perpetual calendar. In 2014, Breitling introduced its own ultra-accurate SuperQuartz calibers, with a patented, thermocompensated design that make them 10 times more accurate than most quartz calibers (albeit not quite as precise as Longines’ VHP movements), i.e., within 10 seconds per year. The brand installs the SuperQuartz movements in its high-tech tool watches such as the Exospace.

Japan’s other large heritage watchmaking house, Citizen, made its own historical contribution in 1976 with the introduction of the first Eco-Drive calibers — quartz movements with rechargeable batteries powered by any light source, from natural sunlight to a lamp on a nightstand. The battery life for those early models was low, so Citizen continued upgrading, releasing a watch in 1986 that could run on a single charge of light for eight days and another in 1995 that ran for six months on a single charge (the modern standard). The first Citizen Eco-Drive watches, powered by the Caliber 7878, were launched in 1996, equipped with the groundbreaking technology that is still at the heart of the Eco-Drive movements today: light passes through a translucent dial with a solar cell mounted directly underneath it, which supplies power to the lithium ion battery of the movement below. From an environmental standpoint, this also means almost never having to discard old batteries and replace them with new ones. Eco-Drive has become the tentpole technology around which Citizen has built much of its modern collection.

Tech Meets Mech in Spring Drive

Around 1977, Seiko began conceiving a new type of watch movement that would combine aspects of both the mechanical mechanisms that the company had been using since the late 19th Century and the quartz-powered ones that it had been so instrumental in pioneering in the 1960s. The Spring Drive movement, which finally made it into a commercial product in 1999, was designed to combine the high torque of a traditional mechanical watch movement with the high precision of a quartz one — in other words, a mainspring-powered watch that can achieve the accuracy of a battery-powered one. It accomplishes this chiefly through the use of a trio of in-house inventions: the Spron 510 mainspring, made of a proprietary high-elasticity material engineered to deliver more power, more smoothly, and for a more extended period, to the regulator; the so-called Magic Lever, affixed directly to the shaft of the rotor for a more efficient winding motion; and the Tri-Synchro regulator, which replaces the escapement and regulates the three types of energy generated by the movement — the mainspring’s mechanical energy, the quartz crystal oscillator’s electrical energy, and the resulting electromagnetic energy that turns the glide wheel, which replaces a traditional balance wheel and rotates uniformly over an electromagnetic coil.

The result is an electromagnetically regulated rate accuracy of around +/-15 seconds per month. In later versions, Grand Seiko would further improve that astounding monthly rate accuracy to +/-10 seconds as it fine-tuned and optimized its Spring Drive technology in subsequent years. Spring Drive watches — which can be found exclusively in the Seiko and Grand Seiko collections — are less accurate than quartz, more accurate than mechanical, and offer an appealing hybrid of micro-mechanical innovation and avant-garde technology that speaks to a growing fan base. 

Pushing Limits in the 21st Century

As with quartz and Eco-Drive, it has been the electronics-obsessed Japanese that have largely taken the lead in pioneering new frontiers in electronic timekeeping accuracy and precision. Casio, the tech titan best known for calculators, cameras, and portable computers, started making watches in 1974 and introduced its seminal timepiece, the G-Shock, in 1983. Since then, Casio has been upgrading the capabilities and overall connectedness of its watches, adding modules for receiving GPS signals as well as radio calibration signals from the six atomic timekeeping stations (often called the “atomic clocks”) around the world — two in Casio’s native Japan and one each in China, North America (at Fort Collins, Colorado), the United Kingdom, and Germany. Basically, Casio’s quartz movements equipped with what it calls “Multi-Band 6” capability can automatically calibrate themselves for the correct time, in the correct time zone, whenever they receive one of these signals. Casio has installed the Multi-Band 6 technology, as well as “Tough Solar,” its own system of light-powered battery recharging similar to Citizen’s Eco-Drive, in many of its G-Shock models as well as in other collections like the sport-targeted Edifice and luxury-oriented Oceanus, which was the first watch to include a Multi-Band 6 module when it was introduced back in 2005. (It’s worth noting that the Germans deserve a shout-out in this category as well: Junghans made the first watch to receive signals from an atomic clock, the Mega 1, in 1990, though it only received signals from a single atomic clock — the one in Frankfurt, Germany — rather than from six of them worldwide.)

In 2008, Japan’s Citizen Watch Company acquired U.S.A.-based Bulova and prompted the development of the company’s most significant invention since the original Accutron movement. Designed to be “the world’s most accurate quartz watch with a continuously sweeping seconds hand,” and used exclusively in Bulova watches, the Bulova Precisionist caliber has an oscillator that vibrates at 262,144 times per second, eight times as fast as a standard quartz crystal, which equates to a precision of +/- 10 seconds per year. The oscillator has three prongs instead of the standard two and functions as a “torsional resonator,” meaning that instead of vibrating back and forth like a standard quartz-watch oscillator, the prongs twist like the strings of an electric guitar. Unlike other high-precision watches that rely on external time signals, like the atomic clocks covered above, or need to be recalibrated after a battery change, Precisionist watches use easily replaceable lithium ion batteries like those in other quartz timepieces. One of the most popular Bulova models outfitted with a Precisionist movement is the Lunar Pilot Chronograph (above), a contemporary re-issue of a watch worn on a NASA space mission in the early 1970s. 

Citizen took its emblematic light-powered technology to a new level of precision with the introduction of Caliber 0100 in 2019. A quartz Eco-Drive movement that calibrates time to an astonishing accuracy of +/- 1 second per year, it is the current record holder for the title of “world’s most accurate.”  Distinguishing itself from Casio’s Multi-Band 6 watches and others, like Seiko’s Astron GPS models, Caliber 0100 achieves this unprecedented feat without relying on synchronized data from satellites or radio-controlled atomic clocks. Instead, Citizen equipped the caliber with new AT-cut-type crystal oscillators, which vibrate at a frequency of 8.4 MHz, in place of the tuning fork-shaped oscillators used in most quartz movements. The former’s frequency is more than 250 times higher than the latter’s. The company also devised clever power-saving strategies for the movement, using materials and designs that can generate the much greater amounts of energy that the new oscillators required while also ensuring the entire mechanism is resistant to outside influences such as temperature variations, gravity, and age degradation. The successful result is dependably stable operation for up to six months on a single light charge, or eight months in its power-save mode. The watch can even continuously monitor and adjust for frequency and temperature shifts once per minute, and will automatically correct the hand positions after the watch is subjected to shocks.

Citizen rolled out Caliber 0100 in three watches, all limited editions, measuring 37.5 mm in diameter and 9.1 mm thick. Two have cases and bracelets made of Citizen’s Super Titanium, both of which are treated with the brand’s proprietary Duratect surface hardening process. The most exclusive of the trio has an 18k white gold case, a cream-colored dial, and a black crocodile leather strap with tone-on-tone stitching. Its elegantly understated dial speaks to the watchmaking motto that it embodies: interior complexity and innovation in the service of exterior legibility and the be-all-end-all of dependable timekeeping accuracy.