Biblical value of pi
The Bible indirectly claims that the value of π (pi) is 3. 1 Kings 7:23 says:
 "And he made a molten sea, ten cubits from the one brim to the other: it was round all about, and his height was five cubits: and a line of thirty cubits did compass it round about."
If a circle has a diameter of 10 cubits, and a circumference of 30 cubits then the value of π is 30 cubits ÷ 10 cubits = 3.00.
Counterapologetics
Atheists often use this passage to demonstrate a mathematical error in the Bible, despite the fact that it is supposedly divinely inspired. Since the circumference of a circle is π × diameter, a round sea could only be ten cubits across and thirty cubits around if π = 3, rather than 3.1415...
This shows that the Bible is not inerrant in such a way that no amount of denying scientific observations can sweep the objection away, because it is based on mathematics, which is much harder to dispute.
Apologetic response
 The circumference may have been the interior circumference while the diameter given was from one outside edge to the other. That is, the thickness of the brim accounts for the discrepancy.
 If you make a molten sea with a circumference of thirty cubits, you'll find that the diameter is 30 ÷ π or 9.55 cubits. Or ten cubits, to round to the nearest integer.
 The Bible does not say that π must be three, unless you are going to assume that the numbers given are accurate to more than two significant figures, which is unjustifiable given the wording.
 Additionally, the Bible doesn't claim that the sea was a perfect circle, only that it was "round" or "circular".
Summation
While some atheists like to cite this as a demonstration against strict Biblical literalists, as we could certainly expect greater precision if the words of the Bible come directly from a god, the argument tends to be viewed as trivial. While the argument can be useful, it would seem to be vastly overshadowed by the wealth of errors, contradictions, ambiguities and atrocities contained in the Bible.
It is also worthy to note the inherent ambiguity of the cubit itself, based off of the length of the human forearm. Our ancient friends did not possess the accuracy of measurement that we do today.
