Find Center of Circle Using a Square

1. Put the outside corner of the square on the edge of the circle.
2. Mark were the edges of the square cross the edge of the circle
3. Connect these two points with a straight line to create a chord.
4. Repeat the first three steps to draw a second chord. This should be at a wide angle from the first chord, ideally ~ 90 degrees.
5. The point where the two chords intersect is the center of the circle.

Find Center of Circle Using Chords and Perpendicular Bisectors

1. Draw two chords on the circle that do not cross.
2. Locate and mark the midpoints of each of these chords.
3. Draw perpendicular lines from the chords at these midpoints.
4. The intersection of the perpendicular lines is the center of the circle.