Let’s get this out of the way first, Seiko’s 6138 - like this all original Seiko 6138-7000 "Calculator" here - was not its first automatic chronograph movement. This honor belongs to the legendary 6139, which was released one year before the 6138.
With that out of the way, the 6138 garners many a mention within Seikoholic circles and it was Seiko’s first two-register model, with 30-minute and 12-hour sub-dials. It also had features the 6139 lacked, like handwinding and its own share of unique nicknames like “UFO,” “bullhead,” “kakume,” and “John Player Special.” But also – and relevant here – the nickname “calculator.”
The6138-7000 calculator is high on the “less seen” scale for 6138 variants, with its slide rule bezel and indicator, akin to contemporary Breitling Navitimers. It features a double external bezel, one fixed and one mobile to perform calculations and to set cursor position. Apart from the calculator function, the 6138-7000 features the same typical elements as all other 6138 chronographs. The calculator rings add some significant size to the watch, reaching 44mm in diameter, so this was a rather impressively-sized watch for the era.
With the 6138 movement, Seiko - as usual - set the standard followed by the Swiss watch industry 20 years later. The same movement configuration was adopted by Rolex when it made its own in-house movement for the Daytona in 2000, 30 years after Seiko released its 6139 and 6138 calibres. Oddly, the 6138 was the successor of the 6139 automatic chronograph movement, and produced in parallel with it until 1979. The 6138 was technically at least equal to its Swiss counterparts, as it featured a fully integrated chronograph vice stacked modules.
There were two versions of the 6138, with the first, the 6138A, introduced in 1970 with 21 jewels. The 6138B – like the one here – was introduced subsequent, and featured 23 jewels. Both had a column wheel that regulated chrono functions, and a vertical clutch mechanism for engagement.
The 6138A/B was a two register chronograph, counting up to 30 minutes on one subdial and another 12 hours on the second dial. All 6138 movements feature a quick-set day/date indicator and can be handwound (unlike the 6139 model), relatively unique for Seiko chronographs of this era. Seiko marketed the 6138 line with the sports enthusiast in mind, with tachymeter ring and distinct markers, and this 6138-7000 calculator is no different.
It comes with a leather strap, NATO strap, Pelican travel case, and springbar tool.
1972 Seiko 6138-7000 Calculator Automatic Chronograph
DIAL: Original Seiko-signed flat black dial, with sunken subdials. Original hands – while the chronograph hands were originally red in color, these have faded with time and exposure to sun to a pleasant off-orange. Day and date work as designed.
CASE: Original 44mm (46mm w/crown) x 47mm lugless stainless steel case, and like other 6138 variants, this case is quite thick at 14.5mm. As noted, these cases also a double external bezel, one fixed and one mobile to perform calculations and to set cursor position. Of note, this 6138 calculator, like many examples, no longer retains its plastic cursor - these were brittle and broke off frequently.
CRYSTAL: Original crystal, no major scratches or blemishes. Among all 6138 models, the 6138-7000 was the only one that originally was equipped with acrylic glass.
BAND: Brown leather strap, with cream accent stitching and stainless-steel hardware. This 6138 also comes with a black NATO strap, also with stainless-steel hardware.
MOVEMENT: Original 6138B automatic movement, manufactured in November 1972.
CROWN: Original unsigned crown.
CHRONOGRAPH PUSHERS: Pushers depress with satisfying click. Chronograph hands snap back and reset to zero with no issue.