Seiko Cal. 6640 - 837

The Seiko 6640-837 represents an important milestone in Seiko's 1981 lineup. Powered by the 6640 caliber with 20j jewels beating at 21,600 bph, it delivers a 37 hours power reserve. [seikata-wm-1410ebb1ff26]

Also known as: Sumo, Tuna

Specifications

Movement

Quartz

Case Material

PVD Black

Case Width

40mm

Case Thickness

13.6mm

Lug Width

21mm

Crystal

Acrylic

Bezel

Bidirectional

Water Resistance

150m

Dial Color

Burgundy

Jewels

20j

Frequency

21,600 bph

Power Reserve

37 hours

Year

1981

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