a reference device for cooperating with the cylindrical part in {HEAD ~ orbital motion} and defining {TAIL ~ a checking condition} of said apparatus 
a reference device for cooperating with the cylindrical part in { HEAD ~ orbital motion } and defining { TAIL ~ a checking condition } of said apparatus
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH