Q: How to find center of a circle?
A: Finding the center of a circle or disc you have punched out can be quite a task. However, using your divider is an easy way to tackle this challenge.
Begin with your circle and your divider. Just eyeballing it, find the approximate center of the circle with your divider. Set your divider to that distance and bracing against the outside of the circle with one leg, draw three intersecting lines using the other leg. If the three lines intersect at a point, you have found exact center! Otherwise, the lines will create a triangle, and some point in the middle of the triangle is your center. Continue making adjustments and drawing lines until you have the exact center.
Please note: the black sharpie mark is not necessary for this process, it is only used for purposes of photography.