It is convenient for {HEAD ~ the user} to know {TAIL ~ the remaining toner}, the photo conductor life, etc 
to know
It is convenient for { HEAD ~ the user } to know { TAIL ~ the remaining toner } , the photo conductor life , etc
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH