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