{TAIL ~ The even field} and {HEAD ~ the odd field} combine to form one frame of TV timing 
{ TAIL ~ The even field } and { HEAD ~ the odd field } combine to form one frame of TV timing
TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH