Rather than trying to immobilize a living, moving organ to place the organ in the fixed frame of reference of a table-mounted robotic device, the present disclosure teaches mounting a robot in the moving frame of reference of the organ. The variable attenuator of the invention is suitable for use in various high frequency and microwave circuits and systems, and has the features of a wide frequency band, small size, easy fabrication, low cost, and so on. In response to an activation state of the other of the manual control device and the automatic control device, the first actuating signal is asserted and a second actuating signal is asserted in stead to adjust the working condition of the vehicular monitor according to the second actuating signal.