一炷香，一盏茶的时间，之所以可以选焚香，喝茶这类活动来计时是因为它们是在古人生活中常见的有共识的活动。

漏壶——分成100刻

天干地支——12个时辰

汉代皇宫中值班人员分五个班次，按时更换，叫“五更”，由此便把一夜分为五更，每更为一个时辰。戌时为一更，亥时为二更，子时为三更，丑时为四更，寅时为五更，其对应如下：
一更天：戌时　19:00 - 21:00
二更天：亥时　21:00 - 23:00
三更天：子时　23:00 - 01:00
四更天：丑时　01:00 - 03:00
五更天：寅时　03:00 - 05:00

铜壶滴漏计时——点。一更分为五点，所以，一点的长度合现在的24分钟。

圭表、日晷——通过太阳投影的移动方向来确定并划分时刻，由晷面和晷针组成，晷面上刻有刻度。

3500 B.C. Sundials come into use.The simplest sundial is a stick in the ground.When the sun shines, the stick casts a shadow. As the sun "moves" from east to west, the shadow moves from west to east. You can tell the time of day by where the shadow is pointing.

滴漏、漏刻——它的原理是利用水从漏壶中滴出，水位下降，壶中的箭刻也下降，从而确定时间或滴水进壶中，水位上升，箭刻上升来指示时间。用水流动来计时。

（水运）浑天仪——东汉张衡，机械时钟，据记载，浑天仪上装有日、月两个轮环，以水击轮，令其自转，浑象转一周即为一天，日便环转1/365周，仪上还装有两个木偶，分别击鼓报刻，这是一个设计十分精妙的机械，媲美现在的挂钟一样准点报时，简单来说就是世界上最早的机械时钟，比西方要早六百年。

1500 B.C. People in Egypt and Sumer develop some of the first water clocks.Unlike sundials, water clocks measure time even when it's cloudy.

（水运）仪象台——它的齿轮机构更加复杂，精度也更高，意义最大的是在仪器上装有一擒纵机构----“天衡”，这一机构可以让齿轮由连续运转转为间隔运转，减少了机械疲劳，又提高了精度。

A.D.1280 Around this time, Europeans build the first mechanical clock using a verge escapement. A special gear makes the clock tick.It's attached to more gears that move a hand around the clock's face to count hours. The ticking isn't perfect, so the clock can be too fast or too slow by as much as an hour every day! Most clocks are machines with an oscillator (something that ticks to mark out equal moments of time) and a counter (something that counts the ticks).
1370-1410 European cities build towers with mechanical clocks inside. Every hour, a bell is rung for all to hear.

1656 Dutch scientist Christiaan Huygens invents the pendulum clock（钟摆钟）.

1927 Warren Marrison and J.W.Horton build the first quartz clock （石英钟）at Bell Laboratories in New Jersey. more evenly

1955 An atomic clock（原子钟） is built in England. It measures oscillations (vibrations) of light from cesium atoms. Atomic clocks are the most accurate clocks yet.

1990s The Global Positioning System, or GPS is a group of 24 satellites orbiting Earth. They carry atomic clocks and can tell the exact time.

Today People rely on internet and cell-phone networks , which need super-precise timing.