A period of extended use, as used in this application, means a period of {HEAD ~ use} of more than about one hour, and generally more than four hours and {TAIL ~ less than twelve hours} 
of
A period of extended use , as used in this application , means a period of { HEAD ~ use } of more than about one hour , and generally more than four hours and { TAIL ~ less than twelve hours }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL TAIL