Even a small variation of frequency can lead to quite considerable frequency errors further on in the circuit.
Almost all modern radios derive their stability from a “reference frequency” circuit, and the frequency counter is essential to ensuring these are correct.
This model of frequency counter is capable of measuring frequencies between 0.01Hz up to 2.4GHz with a variable gate time that may continuously varied from 100ms to 10s.
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 can be changed by movement, interference, or even drift due to age, meaning it might not “tick” correctly.
This can make a frequency reading, when referenced to the timebase, seem higher or lower than the actual value.
Highly accurate circuits are used to generate time-bases for instrumentation purposes, usually by using a quartz crystal oscillator.