said mounting fixtures being capable of inverting a mounting direction of {HEAD ~ said device} relative to {TAIL ~ a second user}; and 
relative to
said mounting fixtures being capable of inverting a mounting direction of { HEAD ~ said device } relative to { TAIL ~ a second user } ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH