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