Regular collection of the background insures {TAIL ~ optimum photometric performance} and increased baseline stability of {HEAD ~ the system} 
Regular collection of the background insures { TAIL ~ optimum photometric performance } and increased baseline stability of { HEAD ~ the system }
OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD