Figure 7.

Time interval measurement.

calibrated periodically, since the drift rate will cause a cumulative

deviation in frequency which can result in a measurement error.

The

accuracy of precision quartz oscillators is usually expressed as long term

stability and short term stability.

Long term stability refers to slow

changes in average frequency with time due to secular changes in the

resonator or other elements of the oscillator. Short term stability refers

to changes in average frequency over a time sufficiently short so that the

change in frequency due to long term effect is negligible.

Four methods

have been developed which extend the digital frequency measuring

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