Abstract: A device for ascertaining the degree of compaction of beds of material with a vibratory compaction device as a function of the vibratory amplitude of the motion of the compaction device at selected frequencies is described. The amplitude of vibratory motion of a compaction device is measured at a fundamental frequency and at least the second harmonic of the fundamental frequency and a ratio of the measured signals is computed. The ratio or quotient of the two signals provides a representation of the degree of compaction of the material being compressed by the compaction device. The ratio or quotient may be utilized either as a direct indication to an operator of the degree of compaction or as a control signal in an automated servo control compaction system.