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