8-4
where f = frequency (= number of “events” per unit time), and
t = period (= time between “events”)
                                             
                                             
                                       
                                                                     
             Frequency source + counting mechanism ® clock
   Examples of frequency sources: the rotating earth, pendulum,
   quartz crystal oscillator, and atomic frequency standard.
Frequency and Time
   The essential parts of a clock are a frequency source (oscillator) and a counting device.