The tractor sensing apparatus 11 wherein {HEAD ~ the sensing means} is {TAIL ~ a Hall effect sensor} 
is
The tractor sensing apparatus 11 wherein { HEAD ~ the sensing means } is { TAIL ~ a Hall effect sensor }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL