The first European clocks were brought to Japan in the second half of the 16th century by Christian missionaries; however, these clocks were not immediately useful as a different system to calculate the time of day was in use in Japan at that time. In the Japanese system, which was roughly based on the lunar cycle, one day was divided into twelve hours, six during the day and six at night.
In the Japanese system the twelve hour day began with the sixth hour, working through five, four, nine, eight, and seven before starting over. The hours one, two, and three were omitted as they were associated with Buddhist prayers. Each hour was also associated with a Chinese zodiac sign. These divisions of six hours were called akemutsu明け六つ, during the day, and kuremutsu暮れ六つ, at night. The division between these was somewhat nebulous as it was based not on the rising and setting of the sun, but rather whether or not there was enough light to work. As daylight and twilight hours would naturally lengthen and shorten with the changing of the seasons, any devices for telling time would necessarily have to be adjusted for these differences.
The solution was the wa-dokei和時計. Unlike a normal clock, which has a clock face with hours divided into set intervals, wa-dokei had a face that could be adjusted over the course of the year. The mechanism to do this automatically took many centuries to develop, but was finally completed in the latter part of the Edo period. It was around this time that the masterpiece of wa-dokei engineering, the Ten Thousand-Year Clock (Man-nen-jimeishou万年自鳴鐘) or more commonly Man-nen dokei万年時計, was created. This ornate and incredibly complex clock featured a planetarium showing the movement of the sun and the moon along with six clock faces: a Japanese clock face, a solar calendar, seven day week calendar, a zodiac calendar, a moon phase calendar, and a European clock face.
Wa-dokei came in a number of styles. Many wa-dokei used weights to drive their mechanisms, much like the European designs they derived from, and therefore were built with stands to accommodate the space required for their movement. One style was the yagura-dokei櫓時計, which was shaped like a belfry or fire watch tower. Another was a more pillar-like shaku-dokei尺時計. As the technology progressed wa-dokei were also incorporated into beautiful inro印籠 carrying cases.
In 1873 the Japanese government declared that Japan would adopt the European calendar and time keeping practices, marking the end of the wa-dokei outside of hobbyists. That however did not mark the end of Japanese clock innovations, and the legacy of the wa-dokei lives on through the watch makers that have made themselves household names around the world through their consistent focus on quality and attention to detail.