Apparently it is exponentiation, compare
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Calculate the International Normalized Ratio using the numbers above as an example. INR=(patient PT/MNPT)^ ISI = (15.2 s/13.1 s)^1.297=1.213. Note: Normal INR should be between 0.8 and 1.3 Low values of INR (less than 0.5 ) indicate a high risk of a clot, while high values (3 to 5) are associated with risk of bleeding.
Read more: How to Calculate INR | eHow.com http://www.ehow.com/how_5108528_calculate-inr.html#ixzz2790CNQ5o
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So, numerically, $15.2 / 13.1 \approx 1.1603,$ then $ 1.1603^{1.297} \approx 1.213. $
If you are not sure how to do the exponentiation, you will need to learn something of logarithms. But my calculator has a button to do it in one step.
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