The clock is a time-measuring device: it shows what hour, minute and second of the day we are in; as a stopwatch, it can measure periods of time and as an alarm clock it can bring people out of sleep. Archaeological finds suggest that people have been striving to measure time since time itself began. In the early days of mankind, people used astronomical phenomena as a guide, read the time of day with the help of simple shadow clocks and used the first calendars for religious purposes. What is particularly interesting, however, is the fact that time measurement developed independently in all cultures. It seems to be an indispensable basic need for human existence to determine the current time and to measure time intervals.