In 1434, inventor
Chang Yŏngsil developed
Korea's first automatic
water clock, which
King Sejong adapted as Korea's standard timekeeper. It is likely that Koreans used water clocks to keep time prior to this invention, but no concrete records of them exist. In 1437, Chang Yŏngsil, with Chŏng Ch'o, created a bowl-shaped
sundial called the
angbu ilgu (), which King Sejong had placed in public so anyone could use it. In 1908, the
Korean Empire adopted a
standard time, GMT+08:30. In 1912, during the
Japanese occupation of Korea, the
Governor-General of Korea changed standard time to GMT+09:00 to align with
Japan Standard Time. However, in 1954, the South Korean government under President
Syngman Rhee reverted the standard time to GMT+08:30. Then in 1961, under the military government of President
Park Chung-hee, the standard time was changed back to GMT+09:00 once again. In order to accommodate
American television viewers, South Korea observed
daylight saving time (GMT+10:00) when Seoul hosted the
1988 Summer Olympics. The one-hour time change meant that many daytime events could be broadcast live from South Korea when it was
prime time on the
U.S. east coast. but the change was reverted to promote Korean unity. ==IANA time zone database==