Seiko Electronic 31-6000 "Horseshoe" – October 1968 | Electric Balance
The defining feature of this Seiko is the expansive steel surface surrounding its round, black dial. Side extensions that wrap around the dial, combined with an opening at the bracelet attachment point, create the distinctive shape that gives this model its name: "Horseshoe." Polished chamfers tracing the edges of the brushed surfaces reveal different facets of the case as the watch is turned.
**IMPORTANT NOTE: As this item is shipped from within the European Union, you will not be liable for any intra-EU customs duties.**
The 36.5 mm steel case features sloping surfaces and lugs that curve toward the bracelet a detail particularly striking when viewed from the side. While the broad surfaces meet polished edges, a small setting crown is recessed into a dedicated cutout on the side of the case.
The black dial features metallic baton indices with a double index at the 12 o'clock position and slender hands. In this layout, which omits a date window, the polished surfaces of the indices stand out clearly against the dark background. The orbital "Electronic" emblem, positioned beneath the "SEIKO" branding, is also repeated on the case back.
Dating to October 1968 (serial number 809574), this piece belongs to Seiko’s first generation of electric balance-wheel watches. The 31EL movement, released by Suwa Seikosha in 1968, utilized a system where energy was drawn from a battery while retaining a traditional balance wheel for timekeeping. This was more than a year before the introduction of the Quartz Astron Seiko’s first commercial quartz wristwatch. Inside the Seiko 31B movement, two battery-powered electromagnetic coils drive a magnetic pallet fork. As the pallet fork advances the gear train, the balance wheel and hairspring regulate the rhythm of timekeeping. The movement also features a "hacking" (seconds-stop) function. Upon opening the case back, one can see the battery, copper coils, jeweled bridges, and the balance wheel, all integrated into a single assembly.
The version without a calendar, featuring a "horseshoe" (U-shaped) case, appears in period catalogs under the reference 31EL 021, paired with a steel mesh bracelet. Its list price in the 1970 Japanese catalog was 40,000 yen. The fine metal mesh bracelet on this particular piece creates a striking contrast with the broad steel surfaces of the case; the clasp bears the "SEIKO" signature.
The watch’s exceptionally well-preserved condition is particularly evident in the craftsmanship of the case. The consistent brushed finish, the narrow polished chamfers, and the sharp, crisp edges around the bracelet attachment points remain perfectly intact. The black dial and the steel mesh bracelet have been preserved with equal care. The watch comes with the Seiko box shown in the photographs.
Final Thoughts
The pristine condition of this 31-6000 model allows for a close examination of the geometry of its "horseshoe" case. With its calendar-free black dial and electromechanical balance movement, it serves as a testament to Seiko’s approach to electronic watchmaking in the late 1960s.
The item you are viewing was manufactured in 1968.
PROFESSIONALLY FULLY SERVICED.
The movement has been completely disassembled; every component has been cleaned, lubricated, and precisely adjusted to ensure flawless operation. (Provided it is not exposed to adverse conditions, it will not require any further maintenance for three years.)
Condition: Tested; all functions are in full working order.
