A system for operating a differential probe which includes a first metal extension and a second metal extension having the same structures is disclosed. Each of the metal extensions includes a rotatable arm, a rotatable base, and a contact end. The rotatable base and contact end of each of the metal extensions extend from two ends of the corresponding rotatable arm at an angle, the contact ends and the rotatable bases of the metal extensions are parallel to each other. The system controls a mechanical arm to adjust a vertical distance between the contact ends to be equal to a required vertical distance by rotating the first metal extension around the rotatable base of the second metal extension clockwise by a rotated angle, and rotating the second metal extension around the rotatable base of the first metal extension counterclockwise by the rotated angle.