Accordingly, {HEAD ~ a relative positioning system} 31 may be used to monitor {TAIL ~ the motion} of the points 122 a 122 c 
used to monitor
Accordingly , { HEAD ~ a relative positioning system } 31 may be used to monitor { TAIL ~ the motion } of the points 122 a 122 c
OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH