Finding the centers of things for woodworking is pretty important. Squares and rectangles are pretty easy, you simply draw two diagonal lines from the opposite corners and the point where they cross is the center of your material.
Finding the center of a circle on the other hand wasn't quite as intuitive to me, and until doing some searching of my own, I didn't know that there was a simple and easy trick. Time to share.
Similar circle finding Instructables can be found here: