The Q value (Quality Factor) indicates the index of goodness of the resonant circuit. In the figure on the right, f0 is the resonance frequency, which is the frequency at which the maximum value of Gain can be obtained. f1 and f2 are frequencies at which a gain of 1/2 that of f0 can be obtained,

It can be expressed as Q= f0/(f2-f1).

LC, RC, and ceramic oscillators have poor frequency stability due to their low Q values, but crystal and SAW oscillators have good Q values, so they have good frequency stability.