, higher frequencies of oscillation are needed. An electronic circuit generates those higher frequencies by multiplying the stable frequency output by the oscillator by some factor. Take the previous example of Ethernet to illustrate. To source the 125-MHz signal to transmit data, a circuit multiplies the output of a 20-MHz quartz os- cillator by 6.25, yielding 125 MHz. Another way to think of it is that for every 4 complete cycles of input from the oscillator, there are 25 complete cycles of output (4 X 6.25). Obviously, a device used to measure a time interval must cycle at a much higher rate than the time interval being measured, and the more accuracy required, the higher the rate. To do otherwise is the equivalent of measuring the size of microbes with a meter-long ruler. So, when engineers need to accurately measure time down to millionths or billionths of a second, they need to use an electronic circuit that cycles at least billions of times per second. Frequency is defined as the number of repetitions of the regularly occurring event over a unit of time. The standard unit for frequency is the Hertz (Hz), defined as the number of events or cycles per second. The frequency of rapidly occurring signals is measured in multiples of Hz, where 1 kHz is one thousand or 103 events per second. Similarly, 1 MHz equals one million or 106 events per second, while 1 GHz equals one billion or 109 events per second. While frequency is the number of cycles per interval of time, the period is the length of time (the duration) for the motion to complete one cycle. One is the reciprocal of the other-a pendulum swinging back and forth twice every second has a frequency of 2 Hz but a period of 0.5 seconds. Mathematically, we describe it as Frequency Oscillators with periods of longer than one second therefore have frequencies of less than 1 Hz. For example, a circuit that cycles once every 10 seconds is 0.1 Hz, once every 1000 seconds is 1 mHz, and once per day is 1/86,400 Hz (11.574 uHz). The oscillator frequency, the rate at 