Finding the Center of a Circle

My son and I were having a conversation about how to find the center of a circle (he's my little aspiring engineer/hacker). While there are many ways to find the center of a circle, this is the one I remembered from high school:

It involves drawing two right triangles inside the circle. Where the hypotenuses intersect is the center of the circle. What is your favorite method of finding the center of a circle?