Halakhah for Eruvin 113:10

And remember with this that the principles that the Sages, may their memory be blessed, set down regarding matters of mathematics - such as that which they said (Eruvin 57a), "Any ell in a square is an ell and two fifths in diagonal"; and so [too,] "Everything that has three handbreadths in its circumference has a width of one handbreadth"; and so [too,] "How much more is a square than a circle? One fourth"; and similar to these principles - they, may their memory be blessed, did not say with complete exactitude, but rather in approximation. And therefore do not rely on it in the division of things among people. And do not wonder, how did they write things that were not exact, since they are men of truth, that God stands in their assembly. As they only needed the calculations for the perimeters of Shabbat or the planting of forbidden mixtures or their planting of trees, and similar to these things; and in this, that which they were not exact about it brings us to a stringency and does not damage any person's money. And nonetheless, they testified in most of these places that the calculation is not precise there. As they said in each and every place according to what is fit about it, "That is that it is not precise, and it is not precise for stringency," and similar to this that they informed us in every place; such that we not attribute lack of concern or knowledge to them in any thing of this. And the rest of the details of the commandment are in [Bava] Batra and in other places (see Tur, Choshen Mishpat 230).