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The Encyclopedia of Horology

Movement record · Japan

Seiko 7S26

Partially verified

Automatic calibre designed for low-cost mass production

Technical specifications

Diameter
Approx. 27.4 mm
Height
Not recorded in the sources consulted
Jewels
21
Frequency
21,600 vph (3 Hz)
Power reserve
Approx. 41 hours
Winding
Automatic without manual winding
Setting
Pendant set with quick-set day and date
Escapement
Swiss-style lever
Balance
Monometallic balance with Diaflex and Diashock
Complications
Day and date, Centre seconds

Identification features

  • No hand winding or hacking in the base version
  • Calibre marked on the rotor

Known variants

  • Later 7S36, 4R and 6R developments

Servicing notes

Cleaning, lubrication, mainspring and pivot work belong with a qualified watchmaker working from calibre-specific documentation. Conserve original parts: replacing a worn component with a modern substitute changes the object, and refinishing plates or dials destroys evidence.

General guidance only. Antique movements should be serviced by a qualified watchmaker.

Historical significance

One of the most widely produced mechanical calibres of the late twentieth century, and the movement that kept affordable automatics available worldwide.

Related photographs

Black Seiko watch close-up
Black Seiko watch close-up — gcardinal from Norway, CC BY 2.0. Wikimedia Commons file page
Dial detail of a Seiko Speed-Timer Chronograph Automatic 6138-0040 ("Bullhead"), 1976
Dial detail of a Seiko Speed-Timer Chronograph Automatic 6138-0040 ("Bullhead"), 1976 — Dnalor 01, CC BY-SA 3.0. Wikimedia Commons file page
Seiko SKX781 Orange Monster diver watch (2026-02-13)
Seiko SKX781 Orange Monster diver watch (2026-02-13) — Olgierd Rudak, CC BY-SA 4.0. Wikimedia Commons file page

No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.

Sources & references

  1. de Carle, D., Watch and Clock Encyclopedia
  2. Period trade material catalogues and calibre reference compilations (edition-dependent)
  3. Published manufacturer technical documentation where available

Where sources disagree, the disagreement is stated rather than resolved silently.