In ancient time there was no clock in order to measure time. In that time they used the hour glass where sand are kept. It is used to measure the time but it didn't used to show the exact time. It also represents the present as being between the past and the future.

In some places the people used to measure the time by the help of the shadow. Slowly by this method people invent the clock. So now we can know the exact time which can help in many sectors. Clock also help to manage the time and to do the work or something in the specific time.