Then, according to the distances d3, {TAIL ~ d4} and {HEAD ~ other known parameters}, the position of the touch point C can be calculated 
Then , according to the distances d3 , { TAIL ~ d4 } and { HEAD ~ other known parameters } , the position of the touch point C can be calculated
OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH