When printing, {HEAD ~ the surface potential} of {TAIL ~ the printing medium} directly below the printing head is acquired 
of
When printing , { HEAD ~ the surface potential } of { TAIL ~ the printing medium } directly below the printing head is acquired
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH