u/chmandaue

Suwa's Twin Quartz is the better-known kind (but different from Daini's) which was in 1978 the first digitally thermocompensated 32 kHz watch.

Two splayed quartz cans of a 9940. Image from TokeiMedic

The secondary quartz acted as an indirect temperature sensor, whose oscillations the movement compared to that of the primary quartz at the circuit level to generate a correction to the rate of the watch whenever it was cooler or warmer than its ideal temperature (for Seiko, 25 degC).

This took advantage of (and in fact bakes in) the (roughly) quadratic nature of the 32 kHz quartz rate curve. Mathematically, the differece between two such parabolas of the same quadratic coefficient is linear. Arranged so that the parabolas intersect at the ideal temperature of the primary quartz, that line (C in blue below) is proportional fo the temperature difference between the primary quartz and 25 degC.

https://preview.redd.it/bmppun8kig0h1.png?width=1236&format=png&auto=webp&s=4b1f42f3b3563e6c33457c71548a11050acfcbae

In fact, the parabola of the secondary quartz could not have exactly the same coefficient, so the corrected watch still have a 'bowed' rate curve (F in green above), but it was flat enough to promise +/-5 s/yr for the most carefully hand-regulated cal. 998x.

It's hard to appreciate today how revolutionary this was in 1978: a practical HAQ movement which was finally much smaller than the mainstream automatics. High end quartz could, and did, overtake automatics in style and comfort, not just accuracy.

https://preview.redd.it/83kuws8fkg0h1.png?width=1456&format=png&auto=webp&s=5dfc8c2fb6e3b582a2e938942f1ee16cf97f651c

Above early 80’s ref. QGA804 (9983-7000) was, per Seiko Design 140: “One of the most fashionable models of the time. The case and bracelet were made of hard material and given a special polish.”

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The primnary inventor of Suwa Twin Quartz was one Yoshikazu Akahane. It's my theory that, without the credibility of TQ on his belt, Akahane would not have had the capital within Seiko to pursue Spring Drive for as long as he did (20 years) without anything to show for it.

Akahane-san rose all the way to be the boss of Suwa movement R&D in 1997. He formed the team finally took Spring Drive to a commercial product, with a Basel prototype by 1998 and actual watches for sale by 1999.

https://preview.redd.it/cgt1swd6kg0h1.png?width=1125&format=png&auto=webp&s=f851631d6111c275f610155d16941d48fea005fb

That background is why Akahane got a special mention during Akio Naito's introduction of Spring Drive UFA at W&W2025. UFA is two of Akahane's inventions coming together: digital TC and Spring Drive.

Read more here: https://chmandaue.substack.com/p/suwas-thermocompensating-twin-quart

My 9256-8010 (QGH-083)

There are two kinds of Twin Quartz thermocompensation (TC).

The Daini kind was a miniaturization of a mid-60s invention by The Marconi Company, that quartz crystals in a parallel circuit would be stable _between_ the temperature peaks of the component crystals.

Diagram from a 1974 improment on the 1968 Marconi patent

Marconi patented it, showing a triple crystal arrangement, mainly for 'mainframe' quartz master clocks of the kind used by TV stations, governments and Rolex.

Suwa Seikosha, seeking a way to deliver both THIN and ACCURATE, simplified this to two crystals, got the power down by a factor 10,000, and delivered a 3.4 mm HAQ in 1978, with day-date, just two years after Piaget's 'thinnest' but only 2 hand and no-date 3.1 mm cal. 7P.

https://preview.redd.it/ek492hej0nzg1.png?width=586&format=png&auto=webp&s=78459a2c6a428cd54ac8635782240e3eaa507898

Rate curve of cal. 9256

Deep dive and Seiko catalog composites here: https://chmandaue.substack.com/p/daini-seikoshas-thermoinsensitive

Daini twin quartz is cals. 9256, 9223, 972x, 964x and finally the mighty cal. 9681 (coming in a single 18KYG model, ref QZZ994).

A chronograph is, at core, something you start NOW and read LATER to see the elapsed time.

What if you wanted to have a chronograph which could record elapsed time for 500 years? What if you were shooting a space probe towards Alpha Centauri at 0.1% of the speed of light, and so needed the chronograph to run for about 5,000 years? How would the Alpha Centurions, if any, read the chronograph?

My answer is to use radioactive decay. For a 500 year chrono,, I found a radioisotope of platinum Pt-193, with a 50 year half-life. After 50 years, half of it turns to iridium. After another 50, only 1/4 is left. After 500 years, 1/1024 would be left.

I'd protect the platinum from damage and engrave the original concentration of Pt-193 on the outside. Applying carbon dating tech, the future 'reader' would figure out how many years ago I started, by measuring how much undecayed Pt-193 there still was, compared to the concentration I stated on there.

The 5,000 year chronograph would need to use a slower-decaying isotope, because 100 halving is so tiny, 8 x 10^-31, there might not even be a single atom of Pt-193 left.

​I wrote it up long-form: https://chmandaue.substack.com/p/eternal-chronographs