This frequency counter is very compact that fits inside RS232 connector. Parts aren’t soldered on any PCB but directly on PIC chip so everything would take minimal space. So frequency counter can be plugged directly to RS232 interface which also provides a power for chip. The only thing you need to do is to start any terminal program and feed signal to input.
frequency counter gives a resolution of 1kHz for MHz range and 1Hz for kHz range. So its simple and can be carried around. If your computer lacks a COM port it can be connected via RS232 to USB converter.