{"product_id":"vintage-seiko-grand-quartz-9940-8000-wristwatch-twin-quartz-1978-brushed-dial","title":"Vintage Seiko Grand Quartz 9940-8000 Wristwatch Twin Quartz 1978 Brushed dial","description":"\u003ch4\u003e\u003cstrong\u003eSPECIFICATION\u003c\/strong\u003e\u003c\/h4\u003e\n\u003cp\u003e\u003cstrong\u003eReference\u003c\/strong\u003e: Grand Quartz QGN010\u003cbr\u003e\u003cstrong\u003eMovement\u003c\/strong\u003e: Twin quartz 9940\u003cbr\u003e\u003cstrong\u003eAge\u003c\/strong\u003e: August 1978\u003cbr\u003e\u003cstrong\u003eCase Size\u003c\/strong\u003e: 35mm\u003cbr\u003e\u003cstrong\u003eCase Thickness\u003c\/strong\u003e: 8.5mm\u003cbr\u003e\u003cstrong\u003eLug to Lug\u003c\/strong\u003e: 41mm\u003cbr\u003e\u003cstrong\u003eLugs\u003c\/strong\u003e: 19mm\u003cbr\u003e\u003cstrong\u003eCondition\u003c\/strong\u003e: Used Seiko watch\u003cbr\u003e\u003cstrong\u003eBox \u0026amp; Papers\u003c\/strong\u003e: No\u003cbr\u003e\u003cstrong\u003eCase Material\u003c\/strong\u003e: Stainless Steel\u003cbr\u003e\u003cstrong\u003eWarranty\u003c\/strong\u003e: 12-Months Warranty\u003c\/p\u003e\n\u003ch4\u003e \u003cstrong\u003ePOINTS TO MENTION\u003c\/strong\u003e\n\u003c\/h4\u003e\n\u003cul\u003e\n\u003cli\u003eIn fantastic pre-owned condition, with light wear from use\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eCase and bezel have some very light scratches and mark\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eWhite vertically brushed dial\u003c\/li\u003e\n\u003cli\u003eServiced Movement\u003c\/li\u003e\n\u003cli\u003eNew battery fitted\u003c\/li\u003e\n\u003cli\u003e\n\u003cspan\u003eQuartz signed crown\u003c\/span\u003e\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003ePaired with an unworn grey leather strap\u003cbr\u003e\n\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003cp\u003e\u003cstrong\u003eTHE WATCH\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eThe Seiko Grand Quartz 9940-8000 is a vintage high-end quartz wristwatch from Seiko’s late-1970s Grand Quartz series, part of the brand’s premium quartz lineup developed during the height of the quartz revolution. It is fitted with Seiko’s Calibre 9940 Twin Quartz movement, which uses two quartz crystals and a temperature compensation circuit to significantly improve timekeeping precision compared with earlier single-crystal quartz movements. This Twin Quartz system allowed the 9940 movement to achieve exceptional accuracy, far surpassing standard quartz accuracy measured per month.\u003c\/p\u003e\n\u003cp\u003eToday the Grand Quartz 9940-8000 is appreciated by collectors of vintage quartz watches and Seiko enthusiasts not just for its historical significance as part of Seiko’s high-accuracy quartz development, but also for its combination of accuracy, build quality, and period-typical styling that reflects Seiko’s technical leadership in the era when quartz fundamentally reshaped the watch industry.\u003c\/p\u003e\n\u003cp\u003e\u003cstrong\u003eTWIN QUARTZ\u003c\/strong\u003e\u003c\/p\u003e\n\u003cp\u003eTwin Quartz is Seiko’s temperature-compensated quartz system, introduced in the late 1970s. Unlike standard quartz watches that use a single quartz crystal, Twin Quartz uses two crystals along with a specialized circuit that compares their oscillations and corrects for temperature-related timing errors. This was important because temperature changes are the main reason quartz watches drift over time, and Twin Quartz was designed to eliminate that issue.\u003c\/p\u003e\n\u003cp\u003eThe way Twin Quartz works is fairly clever: the two crystals are cut so that their frequency shifts in opposite directions when temperature changes. As the temperature rises, one crystal’s frequency increases while the other decreases. The circuit compares the two frequencies and adjusts the output, effectively canceling out the temperature drift. This made Twin Quartz far more accurate than typical quartz watches of the era.\u003c\/p\u003e\n\u003cp\u003eTwin Quartz first appeared around 1978, and it was used mainly in Seiko’s high-accuracy Grand Quartz models. The most famous Twin Quartz movement is the Caliber 9940, which powered watches like this Grand Quartz 9940 and similar references. These watches are now prized by collectors for their technical significance and their role in Seiko’s quartz innovation.\u003cstrong\u003e\u003c\/strong\u003e\u003c\/p\u003e\n\u003cdiv\u003e\n\u003ch4\u003e\u003cstrong\u003eOUR THOUGHTS\u003c\/strong\u003e\u003c\/h4\u003e\n\u003c\/div\u003e\n\u003cdiv\u003e\n\u003cp class=\"MsoNormal\"\u003eThe Seiko Grand Quartz 9940-8000 stands out to me as an understated yet exceptionally well-executed example of Seiko’s golden era of quartz watchmaking. It combines sharp 1970s styling with the precision and durability that made Seiko a leader in high-accuracy quartz technology. The case design and proportions feel clean and deliberate, giving the watch a look that remains effortlessly wearable today. More than anything, it reflects Seiko’s ability to produce technically advanced watches that were designed to be practical, reliable, and elegant in everyday life.\u003c\/p\u003e\n\u003cp class=\"MsoNormal\"\u003eFor today’s collector, vintage quartz isn’t a compromise, it’s a confident, considered choice backed by knowledge, care, and experience.\u003c\/p\u003e\n\u003c\/div\u003e","brand":"Past2PresentWatches","offers":[{"title":"Default Title","offer_id":58095235039619,"sku":"SGQ8980WO","price":395.0,"currency_code":"GBP","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0783\/2397\/4423\/files\/seiko-grand-quartz-9940-8000-front-_2.jpg?v=1779443539","url":"https:\/\/past2presentwatches.com\/products\/vintage-seiko-grand-quartz-9940-8000-wristwatch-twin-quartz-1978-brushed-dial","provider":"Past2PresentWatches","version":"1.0","type":"link"}