d) measuring {HEAD ~ the flow} of {TAIL ~ air} from said second compartment through said outlet means; and 
of
d ) measuring { HEAD ~ the flow } of { TAIL ~ air } from said second compartment through said outlet means ; and
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH