The Babylonians noticed that the position of a shadow changes during the day. So, they fixed a pole in a sunny place and observed its shadow as it moved.The shadow, they discovered, was long at sunrise and gradually got shorter and shorter until it reached a certain point when it began to lengthen again. At sunset the shadow was as long as at sunrise and at noon it was the shortest.
Similarly, the Indians who were studying the movements of the sun, the moon and other planets, developed several simple astronomical instruments like the gnomon, staff, arc, wheel and the armillary sphere.
They cast the almanac, that is, a calendar listing the days, weeks and months of the year, calculated on the basis of the movements of the sun, moon and other heavenly bodies.
Even as early societies measured the year, the month and the day, they felt the need for devices that would monitor and indicate time precisely. Gradually, one development led to another and, as with most things scientific, literary or religious, it was an exchange of ideas and achievements between India on the one hand and West Asia and the Mediterranean world on the other that produced the so called ‘first’ clocks.