In ancient China, people calculated time according to the position of the sun, the moon and stars in the sky. However, such method was not very accurate. Afterwards, by watching the sun, someone designed a kind of time-counter to identify the time—the sundial (rì guǐ 日晷).

The sundial is a round plate, whose surface is carved with 12 degrees indicating 12 hours. And there is a copper needle erected in the center of the sundial’s surface. Under the sun, the shadow of the copper needle moves slowly on the surface with the movement of the sun, that is, when the shadow of the copper needle moves to a certain degree, it is the time that the degree indicates. In this way, the calculation of time is more accurate.

Besides the sundial, people in ancient China also used the copper kettle clepsydra (tong hú dī lòu 铜壶滴漏) to calculate time, because when it is cloudy or at night, the sundial doesn’t function. The earliest clepsydra was copper pot holding water with a small hole at the bottom and a pole with scales inserting in the center. When the water dropped through the small hole, people would determine the time by the scale on the pole with the decline of the water level. And gradually, the clepsydra evolved into a set of four pots, which were placed in order on a four-level wooden stand. The one on the highest level is called “the Sun Pot”(rì hú 日壶), and the other three pots below it are named “the Moon Pot”(yuè hú 月壶), "the Star Pot”(xīng hú 星壶) and “the Water-receiving Pot”(shòu shuǐ hú 授水壶). The Sun Pot, the Moon Pot and the Star Pot all have a hole at the bottom so that water can drop through it and Water-receiving Pot has a gauge inside. The water drops from the Sun Pot into the Moon Pot and then into the Star Pot and finally into the Water-receiving Pot. As more and more water drops into the Water-receiving Pot, the gauge gradually rises due to the buoyancy of water. Thus people could identify the time by observing the very scale of the gauge emerging above the water. The more levels a clepsydra has, the more accurate it is to calculate the time.

The sundial and cooper kettle clepsydra are the important timing devices in ancient China. Their accuracy is amazing and they also provide precious materials for research on the development of science and technology in ancient China.

日晷和铜壶滴漏
      在中国古代，由于没有钟表，人们便根据日月星辰在空中的位置来判断时间。但是这种判断并不准确。后来人们便发明了一种利用太阳测定石刻的定时器——日晷。日晷通常由铜制的指针和石制的圆盘组成。铜制的指针叫做“晷针”，垂直地穿过圆盘中心，起着圭表中立竿的作用，因此，晷针又叫“表”，石制的圆盘叫做“晷面”，安放在石台上，呈南高北低，使晷面平行于天赤道面，这样，晷针的上端正好指向北天极，下端正好指向南天极。在晷面的正反两面刻划出12个大格，每个大格代表两个小时。当太阳光照在日晷上时，晷针的影子就会投向晷面，太阳由东向西移动，投向晷面的晷针影子也慢慢地由西向东移动。于是，移动着的晷针影子好像是现代钟表的指针，晷面则是钟表的表面，以此来显示时刻。

      那时候人们除使用日晷计时以外，铜壶滴漏也是一种重要的计时仪器。开始时使用单只漏壶，后来出现由多只漏壶组成的复式漏壶。壶身上还刻有制作年份和人员的名字。在铜壶滴漏木制底座上自上而下依次安放着日壶、月壶、星壶、受水壶四个铜制大壶，通高２６４．４厘米。日壶中的水以恒定的流量滴入下层的月壶，月壶中的水也以同样的流量滴入到下层的星壶之中，之后星壶中的水再滴入下层的受水壶。受水壶的壶盖正中立有一个铜表尺，上边刻有１２个时辰的刻度。铜尺前放有一个木制的浮箭，木制浮箭的下端是一块木板，叫作浮舟。受水壶中的水随时间的推移而增加，浮舟便托起木箭缓缓上升。将木箭的顶端与铜表尺上的刻度对照，就可以知道当时的时间了。

      铜壶滴漏与日晷一样是我国古代重要的计时工具，它的精确度之高令人惊讶。同时也为研究古代天文、历法提供了准确的参考尺度。