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