You can use materials such as scale, cardboard and double-sided tape to make standard watches. Fold the card paper to make a watch, and then put the watch upright. Fold another piece of cardboard, draw a scale with a scale, make it into a GUI, and tile it. Standard watches are connected with double-sided tape. A standard watch is ready! It is not only convenient to obtain materials, but also simple to make.

The height of the sun changes in different seasons, and the length of the shadow at noon changes in different seasons. Standard watches are designed and manufactured by using this principle. The main function of a standard watch is to determine the position of the winter solstice, and then determine the length of the tropical year. In addition, we can also determine the direction and solar terms by observing the changes of surface shadows.

sundial

The ruler is an astronomical instrument for measuring the length of the sun shadow. The main purpose is to determine the length of the noon sun shadow, so as to determine the solar term, tropical year or solar year. It consists of two parts: rules and tables. The benchmark and pillar for measuring the sun's shadow standing upright on the flat ground are called watches; The rigid plate used to measure the length of the surface shadow in the direction of due south and due north is called Gui. The laurel is flat and graduated, and the table stands on it.

At noon, the shadow of the watch is projected on Guiyu, and the scale on Guiyu can be used to measure the shadow length of the watch. The time measurement accuracy of the standard instrument is proportional to the length of the instrument. For a long historical period, the accuracy of the tropical year determined by China ranks first in the world. Through further research, ancient Chinese scholars have also mastered the length of the sun shadow in the standard table of 24 solar terms.