One reason for this is the limited capability of {TAIL ~ these systems} to actually ensure {HEAD ~ proper performance} of the client clocks 
One reason for this is the limited capability of { TAIL ~ these systems } to actually ensure { HEAD ~ proper performance } of the client clocks
OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH