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