How many digits of π are needed in real life?

If you had a circle the size of the observable universe, and you wanted to compute its circumference with an accuracy equal to the size of a proton, the number of digits of π that you would need is only 43. NASA scientists, for instance, keep the space station operational with only 15 or 16 significant digits of pi… That means that on a day-to-day basis, you can ignore far more of them!