Seiko Cronos

7-digit and 6-digit serial numbers. Sometimes have month-year serial numbers.

Seiko Cronos (C)

Daini Seikosha. 17 jewels, 21 jewels, 23 jewels.

Calibre 5420

E.g. 5420-1990

Made from 1958.05 until at least 1966/1967: serial number 7622746 (SGP case model).

Smallest model 14035, largest model J15009?

Evolved into King Seiko (calibre 5440, starting in 1961.07).

Seiko Cronos special finish

Seiko Cronos Self-Dater (CS)

Calibre 710/5402. From 1961.07. 21 jewels.

Models: 718990 (stainless steel, "WATER PROOF").

Seiko Cronos Special

Calibre 810. From 1962, 23 jewels. A 23 jewel version of the calibre 5440 found in the first King Seikos?