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The Quartz Clock

A sliver of quartz vibrating thousands of times a second runs most of the world's clocks. Here is how it works and where it came from.

By David Ray · clocks.fyi

A crystal that keeps a beat

Quartz clocks rely on the piezoelectric property of quartz. As NIST time expert Michael Lombardi explains, when an electric current is applied to a quartz crystal, it resonates at a constant frequency.

That steady vibration does the job a pendulum or balance wheel does in a mechanical clock. NIST notes that quartz clocks have no gears or escapement to disturb their regular frequency, though the frequency still depends on the crystal's size, shape and temperature.

An electronic circuit keeps the crystal vibrating and counts the vibrations. Every so many counts it sends out a pulse, which either updates a digital display or steps a tiny motor that moves the hands.

In a watch, the IEEE explains, the quartz crystal takes over the job of the hairspring, balance wheel and escapement, the parts that regulate a mechanical watch.

See also: replacing a worn-out quartz movement on OnlineClock.app.

Why 32,768 Hz?

The crystals in most quartz watches and clocks vibrate 32,768 times a second. The number is no accident: it is 2 to the 15th power.

Crystal maker Jauch explains that each simple divider stage in the circuit, a flip-flop, halves the frequency. Chain 15 of them together and 32,768 becomes exactly 1, giving one pulse per second to drive the second hand.

Why not just use a slower crystal? Jauch notes that a crystal's frequency depends on its size and shape, and one that resonated at 1 Hz would be far too big for a watch. The 32.768 kHz parts it describes are tuning-fork crystals, which Jauch calls the classic watch crystal.

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The first quartz clock

The first clock based on a quartz crystal oscillator was built in 1927 by Joseph W. Horton and Warren A. Marrison of Bell Laboratories, according to NIST's Lombardi. Jauch's history gives 1928 for the first quartz-controlled clock, so dates of 1927 and 1928 both appear; NIST's account is the more authoritative.

Lombardi notes that quartz oscillators can reach uncertainties of about 100 microseconds per day, roughly one part in a billion, and his table of timekeeping milestones lists those figures for quartz clocks alongside the 1927 date.

Seiko's road to the wrist

Shrinking quartz to watch size took more than a decade. Seiko's own history says its Seikosha factory completed a quartz clock for broadcasting use in 1958, and in 1959 a development effort called the 59A Project began work on a quartz movement that could run on a 1.5-volt battery.

In 1963 Seiko introduced a quartz tabletop clock called the Crystal Chronometer. At the chronometer competitions of the Neuchâtel Observatory in Switzerland, Seiko quartz timepieces took second to seventh place in the deck chronometer category in 1964, and first to fifth among pocket watches in 1967.

In 1968, according to Seiko, company president Shoji Hattori set his engineers a one-year deadline to produce a commercial quartz wristwatch.

The Seiko Astron, 1969

Quartz reached the wrist on 25 December 1969, when Seiko introduced the Quartz Astron 35SQ in Tokyo. The IEEE, which named it an engineering milestone in 2004, says it followed about ten years of research at Suwa Seikosha, a Seiko group company, by a team led by Tsuneya Nakamura.

According to Seiko, the team had made 20 watches by December 1969. The design was by Kazunari Sasaki of Suwa Seikosha, and Shoji Hattori chose the Astron name.

The Astron combined a quartz crystal oscillator, a hybrid integrated circuit and a miniature stepping motor to turn the hands. It was accurate to within five seconds a month, or about a minute a year. Its crystal ran at 8,192 Hz, as both the IEEE and Seiko state, not the 32,768 Hz that later became standard. The lower figure still suits the same trick of halving: 8,192 is 2 to the 13th power, so 13 divide-by-two stages bring it down to one pulse a second.

Seiko gives more detail. The six-pole stepping motor turned 60 degrees with each electrical pulse, once a second, driven by a coil of copper wire 20 micrometers thick wound 20,000 times. A thermo-variable condenser helped counter the effect of temperature on the crystal.

The movement was 30 millimeters across and 5.3 millimeters thick, the 18-karat gold case 36 millimeters wide, and the watch drew just 18 microamps. A silver battery lasted more than a year, according to the IEEE.

Seiko says the Astron was about 100 times more accurate than a standard mechanical watch. It was a luxury item at first. Seiko gives the launch price as 450,000 yen, while Jauch says 460,000 yen, the cost of a small car; the IEEE quotes 1,250 dollars and says 100 of the gold watches sold within a week.

The Seiko Museum notes that Seiko later disclosed its patents, after which other watchmakers began producing quartz watches. The watch has collected honors since: the IEEE dedicated its milestone on 25 November 2004, and the plaque can be seen at the Seiko Institute of Horology in Sumida, Tokyo. The museum adds that the Japan Society of Mechanical Engineers listed the Astron as Mechanical Engineering Heritage in 2014.

The quartz takeover

Change came quickly. Seiko decided in 1970 to begin mass production of quartz watches, released a calendar version in 1971, introduced what it calls the first women's quartz watch in 1972, and in 1973 launched a digital quartz watch with a six-digit LCD display.

Jauch says that by the mid-1970s quartz watches were already cheaper than purely mechanical ones. By 1982, according to Seiko, quartz watches made up more than half of world watch production, and the IEEE credits the Astron with speeding the shift from mechanical to electronic timekeeping.

Strengths and limits

Quartz is now everywhere: in wristwatches, wall and desk clocks and countless electronic circuits, as Lombardi notes. Jauch observes that quartz watches run far more precisely than purely mechanical ones.

Quartz is not perfect, though. Lombardi points out that it is sensitive to temperature, humidity, pressure and vibration, and that no two crystals produce exactly the same frequency. That is why one quartz watch may gain a little while another, apparently identical, loses.

For the very highest precision, quartz has been overtaken. NIST notes that atomic clocks now substantially surpass it, though quartz remains the everyday workhorse.

See also: choosing a battery-powered wall clock on OnlineClock.app.

See also: the atomic clocks that outperform quartz on OnlineClock.app.

Questions people ask

Why do quartz watches use 32,768 Hz?

Because 32,768 is 2 to the 15th power. A chain of 15 divide-by-two stages turns it into exactly one pulse per second, and a crystal of that frequency is small enough to fit in a watch.

When was the first quartz clock made?

NIST dates it to 1927, built by Joseph W. Horton and Warren A. Marrison at Bell Laboratories. Some accounts give 1928.

What was the first quartz wristwatch?

The Seiko Quartz Astron, introduced in Tokyo on 25 December 1969. It was accurate to within five seconds a month, and its crystal ran at 8,192 Hz.

Why does my quartz clock gain or lose time?

Every crystal's frequency differs slightly, and it shifts with temperature, humidity, pressure and vibration.

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