The indicator is swept over {HEAD ~ the brake block} to detect {TAIL ~ variations} of the inside brake block surface from the specified radius 
to detect
The indicator is swept over { HEAD ~ the brake block } to detect { TAIL ~ variations } of the inside brake block surface from the specified radius
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH