Suwa Seikosha had an 'S' symbol formed by two 'L's, one upright and one upside down, while Daini Seikosha had a more straightforward 'lightning bolt' symbol.
Generally, the Suwa Seikosha offerings are perhaps the more well known Seikos from that era, what with the first automatic chronographs the non-windable 6139 which were first produced in early 1969; the hand-windable 6138, first produced in late 1969, and not forgetting the classic 'Grammar of Design' Grand Seikos with the 61GS movement, circa 1968-71.
But the Daini Seikosha models were no slouches either.
They had FOUR of their own automatic chronograph movements, the 7015/6/7/8, with the 7016 famously powering the square cased 'Monaco', and the transparent dialed 'Time Sonar' models.
Plus they produced the well respected manual wind 45KS King Seikos which went head-to-head with their automatic cousins the 61GS Grand Seikos in the late sixties.
Even earlier, it was Daini Seikosha which produced the iconic 62MAS, Seiko very first professional dive watch, in 1965!
More on the fascinating history of Grand and King Seikos in this essay, and more about the history of the Seiko 36,000 bph Hi-Beat movements here.
Here, allow me to humbly showcase the four Daini Seikoshas that I own.
I was very intrigued to find this 4522-7000 GS Daini Seikosha on sale at Rakuten Japan.
Firstly it was gold-capped - a relative rarity in late 60s Grand Seikos.
Then it had a linen dial, which I absolutely loved, and which was, again, uncommonly found in 60s Grand Seikos.
Lastly, it had what I thought to be a really interesting case design, with the flared, angular, tapering case reminding me somewhat of Darth Vader's Advanced TIE fighter!
To better appreciate the stunning beauty of this unique case in it's original, unpolished form, check out the gorgeous photos in this Swedish post - I truly think the 452x-7000 is the best kept secret in late 60s Grand Seikos!
Sadly, this one had a damaged dial - someone in the past must have tried to scrape off the patina with sandpaper, and it's got a worn, possibly replacement crown.
But no matter - I could not resist what would be my first dress watch, first gold watch, first linen dial, and first Grand Seiko!
Alas, it dated to October 1969 - just two months younger than yours truly!
Next up, a personal grail - still my solitary birth year, birth month watch.
I'd have liked for it to be a Grand Seiko, but this one comes a close second - a gold-capped King Seiko Daini Seikosha 4502-8000 with linen dial, just like it's younger cousin, the Grand Seiko 4522-7000 from Oct 1969 featured above.
I had seen photos of this model before, and I had disliked the case - unlike the distinctive angular case of the GS 4522-7000, I thought this case was fat, chunky and uninspired, but in the flesh, to my pleasant surprise, it has a larger wrist presence than the GS4522-7000!
Sure, it's dial is blemished, but hey, it's the same age as yours truly, and I ain't in too good of a shape myself!
Here it is with it's younger cousin - both from 1969, both gold-capped, both with linen dials!
For my third Daini Seikosha watch, it was back to chronographs, my first love.
I've always taken a liking to this one, the 7017-6050, nicknamed 'Flyback' - there's just such busy detail yet perfect balance between the dial, the rotating inner bezel, and the fixed outer bezel, and also the wonderful contrasting colours of the black and red outer bezel, the orange inner track and chrono hand, and the lovely pale cream lume of the indices.
Like the early 6139-6000s, the case has a little notch to allow easier access to the recessed crown. How cool is that?
Plus how can anyone not adore the absolutely funky bracelet??? =P
These are not particularly difficult to find per se, but not easy to find an all-correct one down to the bracelet.
Mine, dating to Nov 1971, was a particularly fine specimen courtesy of @soultimer - thanks Gabe!
My latest Daini Seikosha acquisition, I didn't even know existed till very recently, when I came across it amongst the awesome French collector @bertnet69's incredible IG posts (if you haven't already checked it out, you should, it'll blow your mind!).
If you thought the 7017 Flyback was busy, this 7015-7010 'Sliderule' is even more so!
This Sliderule features a sunburst charcoal grey dial, raised applied metal indices, a sliver/blue inner track, a movable inner bezel, and a fixed outer bezel; with orange accents on the outer bezel, the chrono hand, and the 'Speed-Timer' script just above the Daini Seikosha 'lightning' logo.
An incredible array of detail and features - it is, afterall, a Sliderule, but it's all perfectly balanced.
Kudos, Daini Seikosha - this may well be my favourite vintage Seiko 5 Sports Speedtimer of them all!
Interestingly, this Daini Seikosha 7017 'Sliderule' shares the same bracelet as the Suwa Seikosha 6139-7010 'Military' with Arabic numerals on the dial.