WHAT THE BRIDGE MEASURES The ESI Model 250-DA Impedance Bridge measures resistance, inductance and capacitance. It also measures the dissipation factor (D) and the storage factor (Q) of inductors and capacitors. Resistance measurements are usually made with direct current because of the increased accuracy and the lack of hum pickup and stray capacitance effects. Resistance measurements can be made using ac, but they may require external reactance compensation. Inductance and capacitance measurements are made in terms of a simple two-element circuit with the same impedance as the unknown. The bridge dials read the values of this equivalent circuit. An equivalent series circuit is used for capacitors and low Q inductors; an equivalent parallel circuit is used for high Q inductors.