The needle 136 and {HEAD ~ the magnetic bar} 132 are separated by {TAIL ~ a predetermined interval}  
are separated by
The needle 136 and { HEAD ~ the magnetic bar } 132 are separated by { TAIL ~ a predetermined interval }
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH