The background program operates in a selected one of several possible modes, one of which waits for data to supplied from an external data acquisition instrument before returning control to the foreground process so that {HEAD ~ the two processes} can operate in {TAIL ~ synchronism} 
The background program operates in a selected one of several possible modes , one of which waits for data to supplied from an external data acquisition instrument before returning control to the foreground process so that { HEAD ~ the two processes } can operate in { TAIL ~ synchronism }
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH REL REL TAIL TAIL TAIL TAIL TAIL