The resonance method in general is covered in the I R E Standards on Piezoelectric Crystals, 1958 . Procedures are described in the Standards on Piezoelectric Crystals, 1957 , and in the literature [ 6 ] - , The transmission method is used for determination of fm, the frequency at minimum impedance of the sample. In addition to this measurement, the present Standard also specifies the measurement of the frequency at maximum impedance fn. A simplification of the transmission network in the 1957 Standard (Fig. 4) may be used in view of the range of parameters found in the ceramics. This simplified circuit is shown in Fig. 1. The signal generator should have an output impedance lower than the minimum impedance of the test specimen.