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