Seiko 4520

	Brand:	Daini Seikosha, Grand Seiko, Seiko
	Family:	Daini Seikosha 45 Stream
	Height:	3.5 mm
	Jewels:	25
	Reserve:	hours
	Frequency:	36,000 A/h
	Winding:	Hand winding
	Diameter:
© Seiko Cal. 4520 was used in Daini Seikosha's Grand Seiko models	Complications:
	Hands:	Central Hour Hand, Central Minute Hand, Central Seconds Hand

Distinguishing Technical Characteristics
Hand-Winding Balance Bridge Balance, Balance at 3:00
Production: 1968 – 1974
1910s	1920s	1930s	1940s	1950s	1960s	1970s	1980s	1990s	2000s	2010s	2020s

Cal. 4520A was a hand-winding Hi-Beat movement produced by Daini Seikosha in the 1960s and 1970s for their Grand Seiko watches. It was an upgrade over Cal. 4420 thanks to the 10 Hz (36,000 A/h) speed. The closely-related Cal. 4500 was used in King Seiko models and was tuned and finished to a slightly lower standard. Some Cal. 4520 movements were tuned and used for Astronomical Observatory Chronometer testing. The similar Cal. 4522A added a date mechanism, while Cal. 4580A was tuned for even better accuracy.

Seiko 45 Stream Overview

Throughout the 1960s, Seiko had two internal operations competing for watchmaking supremacy. Suwa Seikosha, formed in 1959, focused on high-end men’s watches and originated the Grand Seiko line. Daini Seikosha, the historic watchmaking operation for Hattori Seikosha, developed the alternate King Seiko line before creating the famous Grand Seiko Style with the 44GS of 1967.

In 1968, both Suwa and Daini produced a Hi-Beat movement fit for a Grand Seiko watch. The Suwa 6100 stream was an automatic while the Daini 4500 was hand-wound. Both were used in Grand Seiko models until the decline of mechanical watches in that line around 1975.

The Daini Seikosha 4500 stream replaced the respected but slow-beating 4400 stream in King Seiko and Grand Seiko models. The move from 5 Hz to 10 Hz had been a singular technical challenge for Daini, both from a design and metallurgical standpoint. But the movement featured other technical advances as well, including an “instant” date change mechanism.

Compared to the Suwa automatic movement, Daini’s 4500 stream was more elegant in design, with a classic hand-winding look and full balance bridge. It was also notably thinner, giving Daini’s watches a desirable design differentiator.

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