Sentence:  The fraction of exchange was determined as the ratio of the counts / minute observed in the carbon tetrachloride to the counts / minute calculated for the carbon tetrachloride fractions for equilibrium distribution of the activity between the chlorine and carbon tetrachloride , empirically determined correction being made for the <WSD>difference</WSD> in counting efficiency of * * f in * * f and * * f . 
Meaning of the word marked with <WSD> tags:  the quality of being unlike or dissimilar