The accuracy of a frequency counter is strongly dependent on the stability of its timebase. A timebase is very delicate like the hands of a watch, and sometimes if they are changed by movement or slight interference it might not "tick" correctly. In end making a frequency reading, when matched by the coordinates of a timebase, seem higher or lower than usual. Highly accurate circuits are used to generate this for instrumentation purposes, usually using a quartz crystal oscillator within a sealed temperature-controlled chamber known as a crystal oven or OCXO (oven controlled crystal oscillator).
Frequency counters designed for radio frequencies (RF) are also common and operate on the same principles as lower frequency counters. Often, they have more range before they overflow. I/O interfaces allow the user to send information to the frequency counter and receive information from the frequency counter. Commonly used interfaces include RS232, USB, GPIB and Ethernet.