Seikomatic-R 8305-9010 – July 1965 – Diashock 30 Jewels – "WATER PROOF" case back with dolphin – serviced

Thirty jewels. That is the number that sets this watch apart from the Seikomatic family and is virtually non-existent on Japanese dials of the 1960s outside of the top-tier lines. This example from July 1965 has been fully serviced in Japan—including case restoration.

The Seikomatic family

Seiko introduced the Seikomatic line in 1960 with the caliber 603, bringing automatic winding into mass production. From this foundation, an entire family developed over the following years with different levels of technical sophistication, which Seiko denoted with a letter suffix for each.

The Seikomatic-R offered here represents the high-end variant: The caliber 8305 operates with 30 jewels and Diashock shock protection, and displays the date in addition to the time. For comparison: the brand's quality everyday automatics from this period typically had 17 to 21 jewels; 30 jewels were reserved for more complex constructions.

The case back bears the engraving SEIKO · WATER PROOF · S.S. · 8305-9010 with the serial number 5703409, which dates the watch to July 1965. In the center sits the dolphin emblem, which Seiko used during this era to identify water-resistant cases—a detail not found on later case backs. Furthermore, the designation "WATER PROOF" was replaced by "WATER RESISTANT" in the years that followed.

Serviced

The watch was fully and professionally serviced in Japan in the spring of 2026.

Design and character

The silver dial features a fine sunburst finish and applied, multi-faceted baton indices whose edges flash sharply in angled light. The "SEIKO" signature is at 12 o'clock, with "SEIKOMATIC-R / DIASHOCK 30 JEWELS" below at 6 o'clock. The framed date window is positioned at 3 o'clock.

The finely fluted bezel is a defining feature, giving the dial a structured frame and enhancing the watch visually without making it look overly ornate. Together with the inner rehaut ring, it creates a sense of layered depth that is missing from smooth bezels.

The stainless steel case measures 37.7 mm without the crown, with a 42.5 mm lug-to-lug distance and a height of only 10.3 mm—exceptionally thin for a 1960s automatic and an ideal everyday size by modern standards. At 47 grams on the new dark brown leather strap, the watch is effortless to wear.

Condition

Case in good condition after a conservative refurbishment; crystal replaced. A high-quality new Seiko replacement strap has been fitted, which highlights the watch's premium character.

Technical data

• Brand: Seiko
• Model: Seikomatic-R
• Reference: 8305-9010
• Caliber: Seiko 8305
• Movement: Automatic
• Jewels: 30 Jewels
• Shock protection: Diashock
• Functions: Hour, minute, central second, date
• Case material: Stainless steel, case back with "WATER PROOF" engraving and dolphin emblem
• Diameter excluding crown: 37.7 mm
• Lug-to-lug: 42.5 mm
• Height: 10.3 mm
• Lug width: 19 mm
• Weight including strap: 47 g
• Serial number: 5703409
• Dating: July 1965
• Service: Complete overhaul incl. case restoration in spring 2026 in Japan
• Strap: New dark brown Seiko-branded leather strap
• Origin: Japan

For whom?

For collectors who are systematically building a collection of Seiko’s automatic evolution from the 1960s and distinguishing between the variants of the Seikomatic family. For anyone looking for a vintage automatic with a 37.7 mm diameter and a height of only 10.3 mm—a combination that is rarely produced today. And for buyers who value a documented service with case restoration over an untouched "barn find."

Warranty (pre-owned)

This is a pre-owned item. The limitation period for claims for defects (statutory warranty) is 12 months from delivery.

Note

As this is a pre-owned watch, water resistance cannot be guaranteed despite the historical "Water Proof" engraving. To protect the movement, the watch should not come into contact with water or moisture.