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 difference in counting <WSD>efficiency</WSD> of * * f in * * f and * * f . 
Meaning of the word marked with <WSD> tags:  the ratio of the output to the input of any system