The local mean time in Bangkok was originally UTC+06:42:04.
Thailand shares the same time zone with Vietnam, Cambodia, Laos, Christmas Island, and Western Indonesia, as well as parts of Russia.
Thailand declared on 16 March 1920 that people would move their clocks ahead by 17 minutes, 56 seconds on 31 March 1920 to match the time in use in Southeast Asia.
[4] On 1 January 1990, the Cabinet of Thailand appointed the Royal Thai Navy as the official timekeeper for Thailand.
Thai Standard Time is derived from five atomic clocks maintained by the Royal Thai Navy.