<Li> In atomic clocks the controller is an evacuated microwave cavity attached to a microwave oscillator controlled by a microprocessor . A thin gas of cesium atoms is released into the cavity where they are exposed to microwaves . A laser measures how many atoms have absorbed the microwaves, and an electronic feedback control system called a phase - locked loop tunes the microwave oscillator until it is at the frequency that causes the atoms to vibrate and absorb the microwaves . Then the microwave signal is divided by digital counters to become the clock signal . </Li> <P> In mechanical clocks, the low Q of the balance wheel or pendulum oscillator made them very sensitive to the disturbing effect of the impulses of the escapement, so the escapement had a great effect on the accuracy of the clock, and many escapement designs were tried . The higher Q of resonators in electronic clocks makes them relatively insensitive to the disturbing effects of the drive power, so the driving oscillator circuit is a much less critical component . </P> <P> This counts the pulses and adds them up to get traditional time units of seconds, minutes, hours, etc . It usually has a provision for setting the clock by manually entering the correct time into the counter . </P> <Ul> <Li> In mechanical clocks this is done mechanically by a gear train, known as the wheel train . The gear train also has a second function; to transmit mechanical power from the power source to run the oscillator . There is a friction coupling called the' cannon pinion' between the gears driving the hands and the rest of the clock, allowing the hands to be turned to set the time . </Li> <Li> In digital clocks a series of integrated circuit counters or dividers add the pulses up digitally, using binary logic . Often pushbuttons on the case allow the hour and minute counters to be incremented and decremented to set the time . </Li> </Ul>

Who created the first clock in the world