Seiko Vintage Twin Quartz Watch 9721-5050 — Gold-Plated (1980)

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Two quartz oscillators in a 1980 dress watch

This Seiko Twin Quartz watch, reference 9721-5050, produced in March 1980, can be worn equally well by a man or a woman, with a 29.5mm gold-plated case whose octagonal shape — a rectangle with its four corners cut off — belongs to the formal vocabulary of the late 1970s. Its 6.5mm thickness places it firmly in the dress watch category. The crown, golden and fluted, is set into a recess in the case band.

The gold dial features twelve black Roman numerals arranged around the outer edge, with a printed minute track along the perimeter. The center is occupied by a slightly recessed octagonal surface, which echoes the geometry of the case and creates a second frame within the first. The black baton hands stand out sharply against it, accompanied by a very fine golden seconds hand.

What this understated dial does not reveal is the technology that drives it. Caliber 9721 is a Twin Quartz movement: it contains two quartz oscillators instead of just one, the second serving to continuously correct the thermal drift of the first. Seiko thus addressed the main flaw of battery-powered watches of the period, whose rate varied according to wrist temperature. This family of calibers, produced from 1979 to 1981, equipped the brand’s upper ranges.

The movement incorporates two functions absent from ordinary quartz watches: a end-of-battery indicator, which makes the seconds hand advance in two-second jumps when the power weakens, and hacking, which stops the seconds hand when setting the time for exact synchronization. The performance levels highlighted at the time of sale were those originally announced by Seiko; on a forty-five-year-old piece, the observed rate depends on the ageing of the movement and its maintenance.

Three points to note

• Twin Quartz technology — two oscillators instead of one, the second compensating for the thermal drift of the first, reserved for the upper ranges of Seiko.
• End-of-battery indicator — the seconds hand advances in two-second jumps when the battery weakens, preventing it from stopping without warning.
• Case octagonal gold-plated — a rectangle with its four corners cut off, a characteristic design of the late 1970s, with a thickness of 6.5mm.

Why choose a vintage Seiko watch?

Buying a vintage Seiko watch rather than a new model means gaining access to a leading Japanese manufacture at a reasonable budget, with pieces whose construction has proven its durability. Vintage quartz watches from this period are also the easiest to maintain on the pre-owned market: a battery change is enough to get them running again.

Twin Quartz calibers hold a special place among vintage men’s and women’s watches: they represent the height of Japanese watchmaking research at the end of the 1970s, at a time when Seiko was shifting its prestige ranges from mechanical to quartz. This 29.5mm vintage dress watch can be worn equally easily by either, slipping under a cuff without difficulty.

Like all our pre-owned Seiko watches , it has been opened and checked by our watchmakers: verification of the calibre and its consistency with the reference, verification of the serial number, examination of the dial, hands, and case. Each vintage Japanese watch we offer comes with an invoice Atelier Victor serving as a certificate, a one-year guarantee, and guaranteed lifetime authenticity.

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Technical specifications

• Brand: Seiko
• Model: Twin Quartz
• Reference: 9721-5050
• Serial number: 031872
• Year: March 1980
• Origin: Japan
• Gender: Men's and women's watch (Unisex)
• Movement: High-precision Japanese quartz, calibre Seiko 9721 Twin Quartz (double oscillator, hacking, end-of-battery indicator)
• Functions: Hours, minutes, seconds
• Case: Gold-plated, octagonal shape with cut corners (steel caseback)
• Dimensions: 29.5mm (30.5mm including the crown)
• Lug to lug: 36.3mm
• Thickness: 6.5mm
• Lug width: 19mm
• Crown: Gold-plated, fluted, original
• Dial: Gold, black Roman numerals, recessed octagonal centre, original
• Hands: Black baton-shaped, golden seconds hand, original
• Crystal: Mineral (condition 9/10)
• Strap: Black crocodile-style leather, not original
• Buckle: Steel pin buckle, not original

Condition and guarantee

• General condition: Good overall condition. The gold dial is even and perfectly legible, the Roman numerals and hands are intact. The Crystal is in very fine condition (9/10). The gold plating on the case shows visible wear, notably on the upper left corner and the edges, consistent with the age of the piece.
• Water resistance: Not guaranteed (vintage watch)
• Authenticity: Lifetime guarantee
• Mechanical: Quartz movement checked, new battery, guaranteed for 1 year
• Included: Invoice Atelier Victor
• Not included: Original box and papers

Frequently asked questions

What is Twin Quartz technology?
It consists of incorporating two quartz oscillators into the same movement rather than just one. The second continuously measures temperature variations and corrects the drift of the first, which would otherwise be affected by wrist heat and seasonal changes. Seiko developed this approach in the late 1970s for its upper ranges, in a race for chronometric precision that then pitted Japanese manufactures against one another as much as against the Swiss.

How do you know when the battery is running low?
The movement features an end-of-battery indicator: when the power declines, the seconds hand stops advancing one second at a time and begins moving in two-second jumps. This behaviour indicates that it is time to have the battery replaced, without the watch stopping abruptly. It is a function that entry-level quartz movements did not offer.

What is the hacking function?
It refers to the stopping of the seconds hand when the crown is pulled out to the time-setting position. This makes it possible to synchronize the watch to the exact second with an external reference, rather than accepting a deviation of a few seconds. This function was not systematic on quartz watches of the period.

Is a vintage Seiko watch a safe purchase?
It is, provided that authenticity has been established and the condition is described without reservation. Our watchmakers systematically open the case to verify the calibre and its consistency with the reference, and inspect the dial, hands, and all components. Every pre-owned Seiko watch sold by Atelier Victor comes with an invoice serving as a certificate of authenticity, a one-year guarantee, and authenticity guaranteed for life.

Is this piece suitable for a slim or larger wrist?
With a width of 29.5mm, a Lug-to-lug of 36.3mm, and a thickness of 6.5mm, it suits wrists measuring approximately 15 to 19cm. Its compact format and slim profile place it firmly in the dress watch category, and it can be worn equally well by a man or a woman. The Lug width measures 19mm, making it easy to change the strap.

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