[2] Time keeping in North Korea is under the State Commission for Science and Technology.

In 1434, Jang Yeong-sil, a Joseon scientist and astronomer with other scientists, developed Korea's first sundial, Angbu Ilgu (앙부일구; 仰釜日晷) and was put into service as standard time-keeper of the kingdom and began the standard time at Hanyang (Seoul) which was calculated to be UTC+08:27:52.

[3] In 1442, Chiljeongsan, an astronomical calendar system that was created during the reign of King Sejong used Hanyang (Seoul) local time as its standard as it overcame the limitations of previous-made calendars.

[10] The South Korean government officials worried about inconvenience in Inter-Korean exchange and cooperation, including commuting to and from the Kaesong Industrial Region, and further difference of lifestyle between the North and South Korean people.

[9] On 29 April 2018, North Korean leader Kim Jong-un announced his country would be returning to UTC+09:00 to realign its clocks with South Korea.