In a bidirectional power supply device, a DC-DC converter is connected such that the longer an ON time of the first switch becomes, the higher a voltage of a second positive terminal and a second negative terminal becomes. Feedback indica circumferentially located on the ball extending through the target changes in appearance in form or color subsequent to a proper strike of the ball with the foot. The method preferably utilizes an emulsion breaking agent that is a combination of an anionic tensid, a non-ionic tensid and an alkyl polyglycoside tensid. The navigation system can be programmed to measure and display to the surgeon all information relevant to such joint stability testing, including, but not limited to, starting position, maximum joint translation, maximum joint rotation, instantaneous joint translation, instantaneous joint rotation, and instantaneous joint flexion angle.