Grand Seiko 4520-8000 cap gold, hibeat manual wind from December 1970

Maker: Seiko
Model: Grand Seiko 4520-8000 hibeat cap gold
Year: December 1970
Case Material: gold filled
Case Dimensions: 36mm, thickness 9mm including crystal
Case serial: 0D1120
Caliber: 4520A 25jewels 
Service history: December 2023. Currently running at +3.9 seconds/day. 
Lug Width: 18mm
Bracelet/Strap: Beige Togo calf strap by Handdn (pictured)
Box/Papers: none

The Grand Seiko 4520-8000 is a significant timepiece in Seiko’s history, produced by the Daini Seikosha Kameido factory, a subsidiary of the Hattori Watch Company (aka. Seiko). One of its most distinctive features—shared with the date-equipped 4522 model—is its sleek, "Grammar of Design" case, measuring just 9mm in thickness, making it notably slimmer than many mechanical watches of its time.  

This case was designed by Tanaka Taro, Seiko’s first in-house designer, following the Grammar of Design principles that were first introduced in the 44GS, also crafted at the Kameido factory.  

Inside, the watch is powered by the high-precision 4520A caliber, developed entirely in-house by Daini Seikosha. Regarded as one of Seiko’s finest movements, the Hi-Beat caliber 45 was introduced in 1968 and used in both King Seiko and Grand Seiko models. The 45 series, which includes the 4502A, 4500A, 4520A, 4522A, and 4580, is celebrated among enthusiasts for its exceptional accuracy.  

While Hi-Beat movements (36,000 bph) existed prior to 1968—most notably from Girard-Perregaux and Seiko’s own Suwa Seikosha—the caliber 45 was a fully in-house creation by Daini Seikosha. Its significance is further highlighted by its success in the 1968 Geneva watch competition, where a derivative of this movement dominated the mechanical watch category, surpassing renowned Swiss brands like Omega and Longines.

Overall, this timepiece is in well-preserved vintage condition. The case appears to have been polished only a few times in the past, as it remains sharp for a cap-gold case and retains its distinctive Tanaka "Grammar of Design" profile. The original silver-white dial is clean, with an appealing cream patina developing evenly across the surface. The original hands and crown show signs of aging but remain in good shape. The high-beat caliber 4520 movement was serviced by the previous owner and is currently performing exceptionally well, running at +3.9 seconds per day. The case back is in excellent condition, with the original GS gold medallion remaining crisp and well-preserved. The watch comes with a high quality Beige Togo Calf strap crafted by Handdn. 

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