{HEAD ~ a guide member} slidably mounted on {TAIL ~ said head} in a direction parallel to the axis of said measuring element 
slidably mounted on
{ HEAD ~ a guide member } slidably mounted on { TAIL ~ said head } in a direction parallel to the axis of said measuring element
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH