The value of π...?

Again this is one of the curious sides inside of me taking the most of me. How do you anatically determine the value of π? Today, we have computers that can calculate at lightening speed the value of pi, but how do you do it? What is the program?

As a practical excercise you can try to take the dimesions of circular objects - their circumfrence and diameter - and literally calculate the value. But this method has its own limitations. π is irrational - it cannot be expressed as a simple fraction. Of course it takes fourier series to calculate it. And we have to manually calculate it too! But how to make sure that this is the value of π?

This problem has become a puzzle over the centuries. I don't know when will I find an answer to this?