频率计是常用的测量仪器，每单位时间为单位。

代码说明：

频率计是常用的测量仪器，它通过对单位时间内的信号脉冲进行计数，从而测量出信号的频率。设计一个6位频率计，可以测量1～999 999 Hz的信号频率。-Frequency meter is commonly used measuring instruments, which per unit time of the signal pulse count in order to measure the frequency of the signal. 6 to design a frequency counter, can measure 1 ~ 999 999 Hz signal frequency.