or frequency of the oscillator during the decay process while eliminating all implementation dependent deviations of the excitation because this is not applied to the oscillator during the decay measurement furthermore the measurement of the frequency of the oscillator with a frequency comparison measurement can be performed and is very accurate phase drift of the beat amplitude since the excitation is measurement invariable one can rapidly switch between decay and excitation mode several times per second in an advantageous embodiment of the invention it may be provided that the decay process is interrupted after a predetermined time interval or on reaching a predetermined amplitude value and from the obtained amplitude values the quality factor and or the width of the decay window is calculated by extrapolation or the time interval for the decay is held constant or selected therefore the decay process need not be complete because the quality factor can be calculated by extrapolation of the amplitude values even in the case of a small amplitude drop thus the decay window may have a constant with independent of the filling of the oscillator the accuracy of the quality factor measurement thus increases with decreasing quality factor as the difference in amplitude within the constant decay window increases and thus the difference with respect to a constant noise preferably the interval for switching on and off is determined respectively for each oscillator depending on the quality factor and amplitude of the resonance oscillation examined.