First, that's not what I'm doing. I'm looking at a measurement made with a human forearm and deciding it's not a precision measurement. That doesn't require interpretation or any particular position on the accuracy of the text. If I were an atheist who believed the Bible was a collection of fairy tales, I would still think your argument was ludicrous.
Second, believing that everything in the Bible is literally true would mean that one believes there really was a Good Samaritan and that King David really did get comforted by sticks, and it would mean one thinks that Revelation 12 describes a real woman who really wears the Sun for clothing and really rides a dragon. People who say that creationists and others who respect the authority of the Word are "reading it literally" are either putting up a straw man or have no clue what "literally" means.
Third, whether one interprets a piece does not reflect on its accuracy even slighty. One can interpret the author's meaning and intent when reading history, fiction, poetry, marketing copy--anything written, and the fact that one interprets it does not mean that one believes it to be allegorically true, literally true or completely false. It only means one is interpreting.
Actually, you are. If the bible were literally inerrant, it would have been much more precise in calculating the value of the ratio, or, more likely, would have remained silent on the matter.
Allegory is not fairy tale; please do not degrade the argument by referring to it as such.
Oh, and congratulations on the new arrival.