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