Myriad year clock

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Tanaka Hisashige's Myriad year clock, in the Tokyo National Science Museum.

The clock displays Japanese, equal hour, and calendar information.

The Myriad year clock (万年時計, Mannen Tokei^?, lit. Ten-Thousand Year Clock), was a universal clock designed by the Japanese inventor Hisashige Tanaka in 1851. It belongs to the category of Japanese clocks called Wadokei. This clock is designated as an Important Cultural Asset by Japanese government.

The clock is driven by a spring. Once it is fully winded, it can work for one year without another winding. It can show the time in 7 ways (such as usual time, the day of the week, month, moon phase, Japanese time, Solar term.) It also rings chimes every hour. It consists of more than 1,000 parts to realize these complex functions, and it is said that Tanaka made all the parts by himself with simple tools such as files and saws. It took more than 3 years for him to finish the assembly.

In 2004, a project funded by the Japanese government tried to make the copy of this clock. More than 100 engineers joined the project and it took more than 6 months with the latest industrial technologies. However, even with those efforts it was not possible to make the complete copy, such as the brass metal plate used as its spring, before the presentation at Expo 2005.^{[citation needed]}

The original of the clock is displayed at Tokyo National Science Museum, while the copy is at Toshiba Corporation.

The clock, technologically comparable to contemporary Western clocks, was developed through a combination of Japanese knowhow and study of Western sciences ("Rangaku"), during Japan's seclusion period.