Sentence:  Not all the observers have used the same procedures or made the same assumptions about the lunar brightness distribution when reducing the data , and this , together with differences in the methods of calibrating the antennae and receivers , must account for <WSD>much</WSD> of the disagreement in the measured radio brightness temperatures . 
Meaning of the word marked with <WSD> tags:  (quantifier used with mass nouns) great in quantity or degree or extent