Abstract: Improved methods and apparatus for monitoring the delivery of radio frequency (RF) energy from electrodes disposed in tissue for inducing hyperthermia and other purposes. In one form, an impedance display of a power supply comprises an array of discrete light elements, where the number of light elements illuminated increases in response to a percentage increase in calculated impedance. The array of light elements is typically arranged in a non-linear pattern where a left hand portion of the array extends horizontally while a right hand portion extends upwardly. The display allows an operator to visually monitor abrupt increases in impedance between an RF instrument and a target tissue. Such increases are used to determine acceptable power ranges to achieve a maximum sustainable delivery of radio frequency energy to the tissue consistent with complete, rapid, and uniform heating of the tissue.