A frequency counter is an electronic device used to measure the frequency of an input signal. It counts the number of cycles of the signal that occur in a specific time period, usually expressed in hertz (Hz). Frequency counters are commonly used in various fields, including telecommunications, electronics, and physics, to analyze signals and ensure proper functioning of equipment. These devices can be simple handheld units or complex laboratory instruments. They often feature digital displays for easy reading and may include additional functions, such as measuring period or time interval. Frequency counters are essential tools for engineers and technicians working with oscillators, radio frequencies, and other signal sources.