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