A semiconductor switch interrupts output when a microcomputer or an external IC operates abnormally is connected to a control device such, and is turned on or off depending upon a control signal from the control device. In one embodiment, a depth of the cutting blade is sufficient to permit the simultaneous creation of resected surfaces on two bones that articulate, such as both the femor and the tibia for a given condyle, without the need to reposition the guide or the leg. The system further includes logic executable by the processor for accessing the rule base stored in memory, for identifying wheels requiring truing according to the rules in the rule base, and for making wheel truing recommendations according to the rules in the rule base.