According to what can the two sundials of Sheshan Observatory determine the time of day and the weather in four seasons?

According to the direction and length of the sun's shadow. The declination of the sun will change with the seasons. Considering the geographical latitude, azimuth and elevation of the observation point comprehensively, it will change.

However, the sun shadow generally does not have the function of measuring solar terms, and the landlord often uses the standard table instead. There are not only a series of systematic standard tables, but also a group of complex engravings on the ground, which indicate the position of the sun's shadow with different solar terms and different perspectives (if it is astronomical, it will be dizzy).