The relationship between the angle between the sundial and the ground: the angle between the surface of the sundial and the ground is complementary to its latitude. The sundial instrument, also known as the sundial, is an instrument for observing the time of the sun shadow, which mainly specifies the time or minutes at that time according to the position of the sun shadow. It is a widely used timing instrument in ancient China. But there are few records in history books. At present, the earliest record in historical materials is the section of Records of the Han Dynasty: Sima Qian, the official of Taishi, suggested that * * * should be "to set the ceremony and save the inscription", while Records of the Han Dynasty and Arts listed 34 volumes of records of the Han Dynasty, but only retained the title, but

Mathematically, the minimum positive angle formed by the intersection of two straight lines (or vectors) is called the included angle between two straight lines (or vectors), which is usually recorded as ∠ θ (including danger), and the interval range of the included angle between two straight lines is {θ| 0 ≤ θ≤π/2}, and the interval range of the included angle between two vectors is {θ| 0 ≤θ≤π}.