石英風暴時期的傑作
當年市價１０萬日元（見附圖）
9943雙石英錶芯
原裝錶的、錶帶
不反光高透玻璃
底蓋有紀念刻(公司為日本上市公司)
換電極容易，已換上SONY電芯
錶面邊有氧化，無翻寫
殼有小崩, 不影響走時
日曆可選擇顯示日文/英文

以下節錄
Look carefully now at the quartz logo - it is a twin quartz - even more accurate than the regular Grand Quartz! Rated at -10 sec per year.

In 1978, Seiko released the Twin Quartz watch to address the impact of temperature on the frequency of the quartz crystal oscillator, which put a limitation on the accuracy of quartz watch. Seiko put a second crystal in the watch that's linked with a processor that detects the change in temperature and signals the main oscillator to compensate. The result was a huge improve in the watch’s accuracy from 5 seconds per month to 5 seconds per year.

Ref:
http://forums.watchuseek.com/f29/fs-seiko-grand-quartz-aka-grand-seiko-9940-8000-twin-quartz-3109298.html#/topics/3109298?_k=edqtgt

http://forums.watchuseek.com/f366/seiko-grand-quartz-9940-8010-a-797949.html