Often when assembling a machine, putting the head on may take a bit of trial
and error shifting the head back and forth to get the head aligned properly
so the heads bolts will take. This can be greatly simplified by marking the
back of the machine with a short stroke of a permanent marker from the head
to the body before taking the head off. Then, when reassembling, just line
up the two parts of the mark and alignment will be much easier.