Abstract: A circuit is provided whereby varactor diode is placed in parallel with a capacitance of either the sample or reference cell of a dielectric constant detector. At least the circuitry for applying a voltage to the varactor diode is located outside of the oven in which a dielectric constant detector would typically be located. When the same fluid is flowing through both the sample cell and reference cell, the voltage applies to the varactor diode is manipulated until such time as the capacitance of the sample cell and reference cell are substantially matched as seen by the circuitry which processes the output signals from the dielectric constant detector.