Reference number 2 in parentheses indicates {HEAD ~ a second machine frame} which is inverted and is intended for grinding the top sides of {TAIL ~ boards}  
Reference number 2 in parentheses indicates { HEAD ~ a second machine frame } which is inverted and is intended for grinding the top sides of { TAIL ~ boards }
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH