They occur at precise times in programming and can synchronize the operation of receiver station apparatus to {HEAD ~ the timing} of {TAIL ~ programming transmissions} 
They occur at precise times in programming and can synchronize the operation of receiver station apparatus to { HEAD ~ the timing } of { TAIL ~ programming transmissions }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL