The time interval between pulse signals is called period; and the number of pulses generated in a unit time (such as 1 second) is called frequency. Frequency is a measurement name that describes how many pulses appear in a unit time for a periodic cyclic signal (including pulse signals); the standard measurement unit of frequency is Hz (Hertz). The system clock in a computer is a typical pulse signal generator with a fairly accurate and stable frequency. Frequency is represented by "f" in mathematical expressions, and its corresponding units are: Hz (hertz), kHz (kilohertz), MHz (megahertz), GHz (gigahertz). Among them, 1GHz=1000MHz, 1MHz=1000kHz, 1kHz=1000Hz. The time unit for calculating the pulse signal period and the corresponding conversion relationship are: s (seconds), ms (milliseconds), μs (microseconds), ns (nanoseconds), among which: 1s=1000ms, 1 ms=1000μs, 1μs=1000ns .