{HEAD ~ The optical touch device} can avoid a blind zone and can be used as a dual touch device or {TAIL ~ a multi touch device} 
used as
{ HEAD ~ The optical touch device } can avoid a blind zone and can be used as a dual touch device or { TAIL ~ a multi touch device }
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH REL REL OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL