The distance between the center of said sensing chip 31 to {HEAD ~ the center} of {TAIL ~ said wheel body} 11 is represented by r 
The distance between the center of said sensing chip 31 to { HEAD ~ the center } of { TAIL ~ said wheel body } 11 is represented by r
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH