Seiko “Radio Wave Control” Solar – black textured dial from April 2012

SEIKO solar quartz watch
MOVEMENT 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 Seiko’s “Radio Wave Control” Solar Watches

A radio-controlled watch does not so much keep time as check it. Japan’s national time signal, JJY, is broadcast by the NICT on 40 kHz from Ohtakadoya-yama in Fukushima and on 60 kHz from Hagane-yama in Kyushu; between them the two transmitters cover the Japanese islands. A watch built to listen for that signal wakes on its own, usually overnight when interference is lowest, decodes the broadcast time code and pulls its own hands back into line with the atomic clocks that generate it.

Seiko paired that receiver with its solar movement, and the combination is the whole point of the 7B family: the case never has to be opened for a battery, and the time never has to be set. Caliber 7B42 is the plain three-hand, date-only member — automatic and manual reception, automatic hand-position correction, overcharge prevention, an instant-start function, and a power-save mode that parks the hands when the watch is left in the dark. A full charge runs it for about six months of normal use, or roughly a year and a half in power save.

One thing to be clear about: JJY is a Japanese signal. Caliber 7B42 listens for those two transmitters and nothing else — there is no WWVB reception for North America, no DCF77 for Europe, no BPC for China. Outside Japan this is simply a solar quartz watch that you set by hand, rated by Seiko to within ±15 seconds a month while it is running unsynchronised. Inside Japan it is accurate to the second and stays that way without being touched.

About This Watch

The case back reads 7B42-0AS0, with the serial 240272 stamped below it — a Seiko serial that decodes to April 2012. The dial carries its own separate code, 7B42-0BJ4, printed at six o’clock. A dial code that differs from the case reference is ordinary Seiko practice and not a sign of a replacement dial.

Seiko introduced this case on 28 July 2011, in a group of Spirit solar models sold exclusively through AEON group stores in Japan. Three of them ran caliber 7B42, all sharing the same 37.6 mm × 7.8 mm steel case under a sapphire crystal at ¥29,800 apiece; the black-dial member of that trio was catalogued as SBTM149. No model code is stamped anywhere on this watch, so the case reference is what we quote.

The dial is black, finished with a fine woven texture that only shows itself at an angle, and otherwise left almost bare: applied polished baton indices, a printed minute track, a date window at three, and RADIO WAVE CONTROL / SOLAR in small type above six. The inner ring carries four letters — H and L, Y and N. They are the watch reporting back to you: after a reception attempt the seconds hand swings to Y or N to say whether the signal was caught, and to H or L to say how strong it was. Two small pushers sit on the right-hand flank beside the crown, used to trigger a reception by hand and to call up that result.

It comes on its Seiko steel bracelet, seven rows across and tapering to a folding clasp whose cover is signed SEIKO — which is why we can call the bracelet original rather than merely period-correct.

Technical Specifications

• Brand: Seiko
• Line: Not marked on the dial; Japanese dealers catalogue this case under Seiko Spirit
• Reference Number: 7B42-0AS0 (case back) — dial code 7B42-0BJ4
• Movement: Caliber 7B42 — solar-powered analogue quartz with JJY radio time correction; ±15 sec/month unsynchronised, approx. 6 months from a full charge
• Serial Number: 240272
• Production Date: April 2012
• Case Material: Stainless steel, with a matching Seiko steel bracelet and signed folding clasp
• Case Diameter: Approx. 37.6 mm (excluding crown), approx. 7.8 mm thick — Seiko’s published figures for this reference, not caliper-measured
• Dial: Black with a fine woven texture, applied polished baton indices, date window at 3 o’clock, and H/L and Y/N reception indicators on the inner ring
• Crystal: Sapphire — Seiko’s published specification for this reference; not marked on the watch itself
• Case-back: Steel, marked WATER RESISTANT 10 BAR / ST.STEEL / 7B42-0AS0 R2 / MOVEMENT JAPAN / CASED IN CHINA / 240272
• Country of Manufacture: Movement made in Japan, cased in China, exactly as the case back states

Condition Report

The dial is clean and unmarked, the printing crisp, and the applied indices and hands are bright with no corrosion or spotting. The crystal is clear, with no chip and no scratch that catches the light in the photographs.

The case has been worn. The polished bezel and the case flanks carry fine hairlines and a few deeper handling marks, most of them visible around the lugs and along the sides. The bracelet shows the most wear of anything here — scuffs and scratches across the links and over the clasp cover, plus the slight looseness a steel bracelet of this age normally develops. All of it is honest use rather than damage, and the case-back engraving remains fully legible.

This watch has recently been serviced by a professional watchmaker and keeps good time.

Comes complete with original 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.

Why Collectors Want This Watch Today

This is not a rare watch and there is no point pretending otherwise — Seiko sold these in volume through roughly two hundred AEON stores across Japan, to people who wanted a watch that would simply work. What it is instead is one of the least demanding watches Seiko ever built, and that turns out to be worth something.

• Nothing to keep on a schedule. No battery to replace, no winding, no case back opened every couple of years. It charges from ordinary room light and runs roughly six months in the dark.
• The proportions came back into fashion. 37.6 mm across and 7.8 mm thick on a tapering steel bracelet — a size that was considered small for most of the 2010s and is now exactly what people ask for.
• Sapphire and 10 bar on a dress watch that listed at ¥29,800. It will survive a desk edge and it will not mind a sink.
• It never reached shops outside Japan. The AEON exclusivity is a distribution fact rather than a marketing line, which is why these surface abroad only as private imports.
• If you are in Japan, the radio function still works and the watch will hold itself accurate to the second. Everywhere else it is a good solar quartz — we would rather say that plainly than sell you a feature you cannot use.

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We guarantee the item you receive looks and works exactly as advertised — or your money back.

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.