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A frequency standard is a stable oscillator used for frequency calibration or reference. A frequency standard generates a fundamental frequency with a high degree of accuracy and precision. Harmonics of this fundamental frequency are used to provide reference points.
Since time is the reciprocal of frequency, it is relatively easy to derive a time standard from a frequency standard. A standard clock comprises a frequency standard, a device to count off the cycles of the oscillation emitted by the frequency standard, and a means of displaying or outputting the result.
Frequency standards in a network or facility are sometimes administratively designated as primary or secondary. The terms primary and secondary, as used in this context, should not be confused with the respective technical meanings of these words in the discipline of precise time and frequency.