forming a first difference which is {HEAD ~ a function} of {TAIL ~ the actual temperature} and the first model temperature 
of
forming a first difference which is { HEAD ~ a function } of { TAIL ~ the actual temperature } and the first model temperature
OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH