Sentence:  In the lower center rack an 8 - channel recorder indicates the <WSD>percentage</WSD> of carbon dioxide and nitrogen from the upper and lower lobes of one lung , the total volume of inhalation per breath , the flow of air from both lobes , and the pressure of the two lobes with respect to each other . 
Meaning of the word marked with <WSD> tags:  a proportion in relation to a whole (which is usually the amount per hundred)