A is a mechanical clock that has been made to tell traditional Japanese time, a system in which daytime and nighttime are always divided into six periods whose lengths consequently change with the season. Mechanical clocks were introduced into Japan by Jesuit missionaries (in the 16th century) or Dutch merchants (in the 17th century). These clocks were of the lantern clock design, typically made of brass or iron, and used the relatively primitive verge and foliot escapement. Tokugawa Ieyasu owned a lantern clock of European manufacture. Neither the pendulum nor the balance spring were in use among European clocks of the period, and as such they were not included among the technologies available to the Japanese clockmakers at the start of the isolationist period in Japanese history, which began in 1641. The isolationist period meant that Japanese clockmakers would have to find their own way without significant further inputs from Western developments in clockmaking. Nevertheless, the Japanese clockmakers showed considerable ingenuity in adapting the European mechanical clock technology to the needs of traditional Japanese timekeeping. History Clocks have existed in Japan since the mid-7th century AD in the form of water clocks. The Nihon Shoki states that Emperor Tenchi made a water clock, or , in 660 and 671. These clocks were used for another 800 years until the arrival of Christianity in Japan in the 16th century. Christian missionaries were among the first to introduce Japan to Western mechanical spring driven clocks. Francis Xavier, a Spanish Society of Jesus saint and missionary, gave Ouchi Yoshitaka, a daimyō of the Sengoku period, a mechanical clock in 1551. Other missionaries and embassies soon followed, with a mechanized clock being given to Oda Nobunaga in 1569 and Toyotomi Hideyoshi in 1571 by Papal envoys, and two clocks given to Tokugawa Ieyasu, one in 1606 by a missionary and one in 1611 by a Portuguese envoy. The oldest surviving western clock in Japan dates back to 1612; it was given to Shōgun Ieyasu by the viceroy of Mexico (then New Spain). Near the turn of the 17th century, the first Western-styled, mechanical clocks were produced by Japanese natives. Tsuda Sukezaemon is reported to have made a mechanical clock in 1598 after he had examined and repaired many imported clocks on his own. Japanese clock making was facilitated in the 17th century by missionaries living in Japan. Christian missionaries were the first to instruct