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