Frequency is the reciprocal of the signal cycle, which means the number of cycles completed per unit time of the signal. Generally, one second is taken as the basic unit time.

There are many methods for measuring frequency, including passive frequency measurement, comparison method, oscilloscope method, and counting method according to their working principles. The counting method is essentially a comparative method, and the most commonly used method is the electronic counter method. Electronic counter is the most common and basic digital measuring instrument.

Due to the rapid development of digital circuits and the popularity of integrated circuits, counters are widely used. Using electronic technology to measure frequency has a series of outstanding advantages, such as high accuracy, eye-catching and intuitive display, rapid measurement, and easy to automate the measurement process. Therefore, this method is currently the best.