Calculation of Pn and Ps - why we divide by three?

When we estimate number of possible synonymous and non-synonymous changes per codon, why raw counts are not used? E.g., if we take TTT for example - why we do not say that it has one synonymous change per codon, but rather use 1/3 synonymous sites notation?

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written 6.7 years ago by seb85il •

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