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