a light beam scanner within said housing emitting a scanning beam from {HEAD ~ said housing} toward {TAIL ~ a target field}; and 
a light beam scanner within said housing emitting a scanning beam from { HEAD ~ said housing } toward { TAIL ~ a target field } ; and
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH