Mind Blowing Breakthroughs Science show S01 E15 Jang Yeong-sil – History And Principles Of Time Measurement, Part 1

The Baron proposes a show dedicated to time. So he invites a specialist from medieval Korea: Jang Yeong-sil. When the King's guards slept and did not ring the bells indicating different times of the day, the King asked Jang to create a machine that told time automatically. But how did Jang do it?