The objective of this International Standard is to give methods for determining the best representations of modes in quartz crystal resonators by linear equivalent circuits. Circuit representations are based on electrical parameters measured with vector network analyzer equipment using automatic error correction. Determination of the equivalent parameters by the method of this standard is based on the measurement of device immittance in the vicinity of series resonance. The further problem of characterizing the device for operation with a series load capacitance has not been directly addressed, although it is recognized that some applications require such characterization. The same measuring equipment, and fundamentally the same sort of measurement, provides the means to characterize completely the test load capacity fixture as well as the series combination of load capacity fixture and crystal unit.