{TAIL ~ The system} uses {HEAD ~ opposed pointers} disposed on opposite sides of an irradiation center, each pointer including 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 
{ TAIL ~ The system } uses { HEAD ~ opposed pointers } disposed on opposite sides of an irradiation center , each pointer including 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
TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH