Sentence:  Not all the observers have used the same procedures or made the same assumptions about the lunar <WSD>brightness</WSD> 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:  the location of a visual perception along a continuum from black to white