registering {TAIL ~ the clock time} of the day when said change of {HEAD ~ state} occurs at each station; and 
registering { TAIL ~ the clock time } of the day when said change of { HEAD ~ state } occurs at each station ; and
OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH