switch means for producing {HEAD ~ signals} representing {TAIL ~ a selection} of one of said synchronizing devices; and 
switch means for producing { HEAD ~ signals } representing { TAIL ~ a selection } of one of said synchronizing devices ; and
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH