{HEAD ~ The time window} is determined by a window timer which is preset with a number corresponding to {TAIL ~ the opening time} of the window 
{ HEAD ~ The time window } is determined by a window timer which is preset with a number corresponding to { TAIL ~ the opening time } of the window
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH