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