We describe an automatic apparatus for plotting internal friction Q-1 and sample resonant frequency as functions of strain amplitude. Q-1 is measured from the ratio of driving force to strain amplitiude, while the sample is held at resonance by a phase-locked loop and the strain amplitude is automatically varied following a chosen function of time. This method allows contiuous Q-1 measurement, while an appropriate choice of the amplitude variation rate ensures that the measured Q-1 corresponds to a definite strain amplitude rather than being averaged over an amplitude interval as is the case with other techniques. The system incorporates a resonance apparatus which employs an electrostatic drive without DC bias, but any type of resonance appparatus can be used with minor adjustments. The ranges of Q-1, strain amplitude and operating frequency are those of the resonance apparatus employed.