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 {HEAD ~ control} to {TAIL ~ the foreground process} so that the two processes can operate in synchronism 
to
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 { HEAD ~ control } to { TAIL ~ the foreground process } so that the two processes can operate in 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 HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH