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