whereby, {TAIL ~ a transmitter} and {HEAD ~ a receiver} received in said recess means can be pressed against diametrically opposite surface areas of a body protruding part 
whereby , { TAIL ~ a transmitter } and { HEAD ~ a receiver } received in said recess means can be pressed against diametrically opposite surface areas of a body protruding part
OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH