When {HEAD ~ the aperture size} defined by {TAIL ~ the sectors} 12a and 12b reaches the aperture value A, i.e., when N=A, then that terminal of AND gate 45 associated with comparator 43 receives low level signal  
When { HEAD ~ the aperture size } defined by { TAIL ~ the sectors } 12a and 12b reaches the aperture value A , i.e. , when N = A , then that terminal of AND gate 45 associated with comparator 43 receives low level signal
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL 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 OTH OTH OTH OTH OTH OTH OTH OTH