The principle of sundial (the simpler the better) (fast, extra points)

How the sundial works: When the sun rises and sets in the west, the shadows of the objects it shines will move with it. In ancient times, people learned to calculate time and discovered the sundial by observing this natural phenomenon.

The sundial is the oldest time measuring instrument using the shadow of the sun, and now it has become a symbol of human civilization. China has a long history and developed culture, and it is also one of the earliest civilized countries in the world to use sundial timing. So far, the earliest stone carving sundial found in China is a relic of the early Western Han Dynasty, with a history of about 2,200 years. In the history of many ancient scientific and technological achievements in China, the sundial made and applied by the principle of solar shadow timing can be said to be a shining pearl. ?

The main contents include: overview of sundials, astronomical knowledge, descriptive geometry, line drawing design of various sundials and overall design of sundials. The author of this book is a professor at the School of Mechanical Engineering, Shanghai Jiaotong University. On the basis of expounding the origin and significance of sundial, this paper focuses on the design of dial diagram, the core problem of its design. According to the law of the earth's movement, various types of sundial maps are comprehensively analyzed and studied by using the knowledge of descriptive geometry and analytic geometry. Among them, the design formulas and derivation process of various types of sundials are given, and the types of sundials can be drawn conveniently by using these formulas.