This paper presents an evaluation of the RIV circuits used for the measurement of partial discharges. The results show that the NEMA 107-1964 RIV circuit, as presently used in high voltage laboratories, does not consider the entire calibration problem. The test circuit can produce resonance at a particular frequency, the choke coils can create a resonance shift, and the capacitance from the bottom end of the coupling capacitor to ground is significant. This capacitance, combined with the coupling capacitor and inductance of the conductor, forms a resonant circuit at the measurement frequencies.