Abstract
In the past there were many kinds of timepieces in regular use. They can be divided into two types as follows
1) Timer : timepieces to measure an amount of time
2) Clock : timepieces to synchronize social actions
Before the modern society a timer couldn't be used as a clock because of high costs and the difficulty of maintenance. On the contrary, a clock couldn't use as a timer. Even the weight-driven clocks in the Middle Ages hadn't the long hand yet so they hardly clocked a small amount of time. Therefore we could say that these two kinds of timepieces had almost no substitutability in time-keeping.
The biggest change in the history of time-keeking occurred when a pendulum was adopted in the escapement of machine clocks. The clock with a pendulum was so precise that it could measure a small amount of time in proper. Since then the timers were beginning to be substituted by the clock and most of them has disappeared. As the result the two kinds of timepieces were unified into a single one that we can call “the modern clock.”
After this unification the dial of the clock has been used as a scale measuring an amount of time. Then the units of the clock, that is, hours, minutes and seconds, began to be used as the units of an amount of time. The unification of two timepieces led to the unity of the scales of the timer and the clock.
The establishment of the universal scale in timekeeping has advanced the modern sciences and technologies. By this precise scale, the rest-time measuring until a certain time has been possible and the synchronized social system in countdown style has realized. The unification of time peaces is one of the indispensable conditions of the modern society.
