Method for calculating impedance and apparatus utilizing same

A method for calculating the impedance in a first circuit coupling a first radio frequency electrode to a radio frequency controller where the first electrode is disposed in tissue in the vicinity of a second radio frequency electrode coupled to a second circuit. The impedance IMP of the first circuit is measured when energy is being supplied to both electrodes. The impedance IMP0 of the first circuit is also measured when energy is being supplied to the first electrode but not to the second electrode, and subtracted from the impedance value IMP to determine a delta value IMP. The impedance IMP of the first circuit is then measured when energy is being supplied to both electrodes. The impedance delta value IMP is subtracted from the impedance value IMP to arrive at a calculated impedance value for the first circuit. A computer-readable memory and apparatus utilizing the method are provided.