Sentence:  Not all the observers have used the same procedures or made the same assumptions about the lunar brightness distribution when <WSD>reducing</WSD> the data , and this , together with differences in the methods of calibrating the antennae and receivers , must account for much of the disagreement in the measured radio brightness temperatures . 
Meaning of the word marked with <WSD> tags:  simplify the form of a mathematical equation of expression by substituting one term for another