 determining, by the motion coordinate calculator, whether {HEAD ~ or not an X axis motion vector} corresponding to {TAIL ~ the calculated X axis motion} has a value of zero 
corresponding to
determining , by the motion coordinate calculator , whether { HEAD ~ or not an X axis motion vector } corresponding to { TAIL ~ the calculated X axis motion } has a value of zero
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH