Description
SEIKO vintage mechanical watch
MADE IN JAPAN
“Seiko” (精工) is a Japanese word meaning “precision,” “exquisite workmanship,” or “refined craftsmanship.”
It comes from the characters:
- 精 (sei) – fine, precise, refined
- 工 (ko) – craft, workmanship
Originally, Seiko’s watchmaking division was called Seikosha (精工舎), meaning “House of Precision.”
The name first appeared on a watch dial in 1924, shortened from Seikosha and keeping the core meaning; the company itself was renamed Hattori Seiko in 1983 and Seiko Corporation in 1990.
So the brand name literally ties directly to the idea of precision engineering—which is exactly what the company wanted to be known for in its watches.
About the Seikomatic Slimdate Line
🕰️ The Seiko Seikomatic line was a flagship series of high-quality automatic watches produced primarily throughout the 1960s. It represented Seiko’s transition into the modern era of self-winding timepieces, and sat at the top of the company’s mainstream automatic ranges.
The Name: It’s a portmanteau of “Seiko” and “Automatic.” At the time, automatic winding was a high-tech feature, so Seiko branded these watches to highlight that they didn’t need manual winding.
The Design Philosophy: Seikomatic was designed for the “modern business professional” of the 1960s. Its most iconic design choice was the recessed crown at the 4 o’clock position. These early Seikomatic calibers cannot be wound by hand at all — the crown sets the time and the date and does nothing else — so Seiko tucked it down and out of the way to create a sleek, “crownless” silhouette that wouldn’t snag on shirt cuffs.
The Slimdate: Thinness as a Statement. Introduced in 1963, the Seikomatic Slimdate was exactly what its name promised — the slim, date-equipped member of the Seikomatic family. It ran on the caliber 840, a 30-jewel automatic with Diashock protection beating at 18,000 bph, designed at Seiko’s Suwa factory to sit noticeably thinner on the wrist than the standard Seikomatics of the day. The movement proved good enough to outlive its own name: in Seiko’s mid-1960s renumbering it became the caliber 8305, the slim 83-series family that went on to power the Seikomatic-R.
The Slimdate is where Seiko worked out the “thin automatic dress watch” formula it would keep refining for the rest of the decade — a watch that wound itself, showed the date, and still disappeared under a shirt cuff.
About This Watch
This is a Seikomatic Slimdate reference 840990 in stainless steel, produced in November 1963 (serial 3N00530). The silver sunburst dial is signed Seikomatic slimdate beneath the printed Seikomatic emblem, with applied faceted hour markers, a framed date window at 3 o’clock and the 30 JEWELS DIASHOCK designation above 6 o’clock. A finely toothed inner ring adds texture around the dial’s edge, and the crown sits recessed at the 4 o’clock position — the signature Seikomatic detail that keeps the case silhouette clean.
Under the case-back — engraved Seikomatic slimdate 84099 SS on the outside, with the case code SS 840990 JAPAN and the serial stamped inside — works the caliber 840 itself, its rotor signed SEIKOMATIC 30 JEWELS SEIKOSHA 840 — photographed open in the gallery so you can see exactly what you are getting.
The watch comes on a vintage stainless steel bracelet. Its clasp carries a stamp that is not legible in these photographs, so it is described here as a vintage bracelet rather than a confirmed factory original.
Technical Specifications
- Brand: Seiko
- Line: Seikomatic Slimdate
- Reference Number: 840990
- Movement: Automatic caliber 840 (Seikosha), 30 jewels, Diashock, 18,000 bph, no hand-winding
- Serial Number: 3N00530
- Production Date: November 1963
- Case Material: Stainless steel
- Case Diameter: Approx. 36mm (excluding crown)
- Dial: Silver sunburst, applied hour markers, date at 3 o’clock
- Crystal: Acrylic
- Case-back: Stainless steel, engraved Seikomatic slimdate 84099 SS outside; case code SS 840990 JAPAN and the serial stamped inside
- Country of Manufacture: Japan
Condition Report
The dial is the strongest part of this watch: the silver sunburst is clean and even, with crisp printing and only pinpoint age marks visible under magnification. The applied markers and hands are bright, with no corrosion. The stainless steel case shows light hairlines from normal wear, and the case-back engraving remains fully legible. The acrylic crystal is clear. The vintage bracelet shows honest wear, with some patina settled into the fluted center links (see photos); the clasp closes securely. The date advances and frames correctly in its window at 3 o’clock.
This watch has recently been serviced by a professional watchmaker and keeps good time.
Comes complete with vintage steel bracelet*.
(*)Note: Stock bracelets are often shortened by previous owners and may not fit you(see bracelet size in the product images). We match the strap to this watch’s lug width, so there is nothing for you to measure — just pick a padded leather strap for Seiko from the options at the top of the page.
This watch ships from 🇺🇦 Ukraine with tracking number
Why Collectors Want This Watch Today
The Slimdate carries a 30-jewel Suwa movement — caliber 840, renumbered 8305 in the mid-1960s Seiko reorganisation and later used in the Seikomatic-R — inside the recessed-crown Seikomatic case. What the 830/840 family achieved was height: it took several millimetres off the earlier caliber 603, which is what made the slim case possible. This example is the stainless 840990 variant, dated November 1963, from the first year of Slimdate production, and it has already been through the hands of a watchmaker.
Modes of payment:
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We guarantee the item you receive looks and works exactly as advertised — or your money back.
Seiko lug-width matched leather straps — 18 / 19 / 20 mm
About the watch factory
Seiko Group Corporation (セイコーグループ株式会社, Seikō Gurūpu kabushiki gaisha), commonly known as Seiko, is a Japanese maker of watches, clocks, electronic devices, and semiconductors. Founded in 1881 by Kintarō Hattori in Tokyo, Seiko introduced the world’s first commercial quartz wristwatch in 1969.
Seiko is widely known for its wristwatches. Seiko is one of the few watch companies that is fully vertically integrated. Seiko is able to design and develop all the components of a watch, as well as assemble, adjust, inspect and ship them in-house. Seiko’s mechanical watches consist of approximately 200 parts, and the company has the technology and production facilities to design and manufacture all of these parts internally.
Seiko offers one of the widest ranges of watch technologies in the world—quartz, kinetic, solar, mechanical, and Spring Drive—spanning everything from affordable everyday pieces to six-figure haute horlogerie. Over the decades it has launched multiple global brands, including Lorus, Pulsar, and Alba, while elevating its prestige through innovations like Spring Drive, which helped push Seiko into higher-end territory. In 2017, Grand Seiko was spun off into its own standalone luxury brand, while Credor remains part of Seiko’s own lineup, sold primarily in Japan. Seiko’s own global lineup now includes Grand Seiko, King Seiko, Prospex, Astron, Presage, and Seiko 5 Sports.
Among Seiko’s key lines, Seiko 5 (born in 1963) is the gateway mechanical series known for durability and value; Lord Matic defined 1970s style with faceted crystals and colorful dials; Astron remains Seiko’s flagship GPS-solar tech line; Presage focuses on traditional mechanical craftsmanship with enamel and urushi dials; and Prospex delivers professional-grade dive, field, and pilot watches often embraced by enthusiasts. At the top end, Grand Seiko emphasizes precision, Zaratsu polished design, and movements like Spring Drive, while King Seiko—revived in the 2020s—brings back sharp, elegant 1960s styling with modern calibres.
Finally, Credor represents Seiko’s pinnacle of artisanal watchmaking, producing low-volume pieces in precious metals and showcasing Japanese decorative arts and haute complications from the Micro Artist Studio. Beyond watches, Seiko has also produced various electronic devices and, historically, jewelry and eyewear—though those divisions have since shifted to other companies.
