Japanese Domestic Market (JDM) variations: A. ‘5Sports Speed-Timer’; B. ‘Speed-Timer’; World Market variations: C. Chronograph Automatic w/ black dial; and D. Chronograph Automatic w/ brown dial
Seiko is part of a select group of watchmakers in the world that has produced all of its components in-house throughout the entirety of their existence. The Seiko 6138-0040 came equipped with two Seiko original inventions. The first of which is an unbreakable alloy known as “diaflex” that was used as the material for its mainspring. Secondly, a system known as “diashock” was first implemented by Seiko in the 1960’s. These innovations are now fixtures installed in most of Seiko’s watches to this very day. [4]
The 6138 movement was developed by Suwa Seikosha, a branch of the Seiko corporation, as evidenced by the Suwa logo located on the dial at the 6 o’clock position. [6] Although touted as the successor of the 6139 movement, both were manufactured until 1979. The significance of both these movements to Seiko’s history cannot be stated enough, as these gave them the honour of creating the world’s first automatic chronograph movement that features a column wheel and a vertical coupling mechanism. There were also 2 versions of the 6138 movement; 6138A with 21 jewels, and 6138B with 23 jewels. Both versions were classified as 2 register chronographs, equipped with a manual wind day/date indicator. The specifications for both versions are a height of 7.9mm and a movement diameter of 27.4mm, allowing them to accurately measure up to ⅙ of a second, or 21,600 beats per hour. Seiko successfully mass produced the layout for the column wheel and the vertical coupling mechanism, which later on became mainsteam, and was adapted by Rolex for the development of the in-house movement that they would use on the Daytona. This would come about some 3 decades later, a testament to the innovative advancements offered by the Seiko brand to watchmakers the world over. [3]
Slight difference on tachymeter color depending on variation (Left to right: JDM Speed-Timer, JDM 5Sports Speed-Timer, Chronograph Automatic w/ brown dial, Chronograph Automatic w/ black dial)
