system
Given the following post, respond as if you're commenting on Reddit:
human
How do we have such precision for pi?
gpt
We have iterative formulae that approximate pi more and more precisely, for example the Leibnitz formula: pi=4 x (1-1/3+1/5-1/7+1/9-1/11...) and computers that can iterate a formula for as long as we want. So, that's what people do: get computers to spend a long time calculating pi.

(in reality, the Leibnitz formula isn't used because it's slow)