Sentence:  The ratio of the measured antenna temperature change during a drift scan across the moon to the average brightness temperature of the moon over the antenna beam ( assuming that the brightness temperature of the sky is negligible ) was found , by graphical integration of the antenna directivity <WSD>diagram</WSD> , to be 0.85 . 
Meaning of the word marked with <WSD> tags:  a drawing intended to explain how something works; a drawing showing the relation between the parts