Citizen Watch Co Ltd will release what it claims is the world's most accurate quartz wristwatch in the fall of 2019.

It is a solar-powered wristwatch priced at ¥1.8 million (excluding tax). Its product name is "The Citizen."

"We employed a wristwatch technology that enables to most accurately mark the passage of time in the world," Citizen said.

By using parts that were formed with a high accuracy, Citizen developed the "Caliber 0100" watch movement, whose margin of error is only ±1 second per year. The annual margin of error of the company's existing solar-powered quartz wristwatches is ±5 seconds.

"The Citizen" solar-powered quartz wristwatch. With the added value (margin of error: plus or minus 1 second per year), it is priced at 1.8 million yen. (source: Nikkei xTech)

For the wristwatch, Citizen formed gears and springs by using UV-LIGA (Lithographie Galvanoformung und Abformung) process, a MEMS (micro-electro-mechanical system) technology. The company made molds of ultraviolet (UV) curing resin by photolithography using UV light. With the molds, minute parts having three-dimensional structures are made by electrocasting.

With this method, the "third gear," "fourth gear," "fifth gear" and "third return gear" were formed. The third return gear has a structure combining a gear and spring, and the spring is formed by using the UV-LIGA process. The process enables to make parts having small eccentrics with a high accuracy, compared with conventional parts made by cutting and pressing.

Four gears were made with a high accuracy by using the UV-LIGA process (left). The third return gear reduces backlash (right). With a structure combining a gear and spring, the tooth plane is pressed by using the spring so that the backlash is moved to one side. (source: Citizen)

The third return gear is a part for reducing backlash (looseness between tooth planes when gears mesh with each other). The third return gear is pressed in the direction opposite to the moving direction of the gear by using the force of the spring so that the gap (backlash) is moved to one side. It prevents the hands of the wristwatch from shaking.

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