The system uses opposed pointers disposed on opposite sides of {HEAD ~ an irradiation center}, each pointer including {TAIL ~ a light projecting portion} for projecting a beam aimed at the irradiation center, a light receiving portion for generating a detection signal, and a control portion 
The system uses opposed pointers disposed on opposite sides of { HEAD ~ an irradiation center } , each pointer including { TAIL ~ a light projecting portion } for projecting a beam aimed at the irradiation center , a light receiving portion for generating a detection signal , and a control portion
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH