By observing the change in the length of tree shadows throughout the day, people from both the East and the West sought tools to record these variations. In China, the predecessor of the sundial was the “Gui” (a vertical rod) and the “Biao” (a horizontal platform), which have been used to measure seasonal changes and determine the length of the year. The development of the sundial evolved from simple vertical scales to more complex circular designs, such as the equatorial sundial, which has a scale parallel to the equator and utilizes the Earth's rotation and orbit to provide accurate time readings. Other types of sundials, such as the horizontal and vertical sundials, also played a role in various regions of the world, reflecting regional adaptations based on latitude and usage. Advances in sundial technology include the “Yanggong” sundial from the Yuan Dynasty in Korea and the “Tower of the Winds” from ancient Greece, which combined time measurement with the determination of solar terms. These innovations not only enhanced the accuracy of timekeeping but also promoted agricultural planning and scientific research in the ancient society.

Jiaxu Liu. The Mechanism and Application of Ancient Astronomical Time Measuring Tools. The Frontiers of Society, Science and Technology (2025), Vol. 7, Issue 2: 1-8. https://doi.org/10.25236/FSST.2025.070201.

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