In ancient times people do not have watches, can only rely on the height of the sun to roughly judge the time. Later, people found the sun in a large stone slowly moving. And the position of moving every day are the same, so they made a stick on the big stone, and around the stick carved some lines, the sun came to which line, you know the time to work or eat, and this is the world The earliest bell, called sundial. The sun every day is Dongsheng West, the sundial sun on the shadow of the stick every day as the center of the right rotation. Later, according to the sundial way of time to invent the mechanical clock, with a pointer instead of the shadow of the sun. So the clock pointer also like the sun shadow, from left to right to indicate the time.