{HEAD ~ Arrays} of {TAIL ~ such sensors} are constructed with at least two sensors having different chemically sensitive resistors providing dissimilar such differences in resistance 
of
{ HEAD ~ Arrays } of { TAIL ~ such sensors } are constructed with at least two sensors having different chemically sensitive resistors providing dissimilar such differences in resistance
HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH