Sentence:  Not <WSD>all</WSD> 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 much of the disagreement in the measured radio brightness temperatures . 
Meaning of the word marked with <WSD> tags:  quantifier; used with either mass or count nouns to indicate the whole number or amount of or every one of a class