The method of drawing a perpendicular bisector using a rope. Take two points A and B on a line, and take a rope longer than the distance between the two points. Mark the mid-point M of the rope by folding it in half. Now hold the two ends of the rope at the two points on the line, and stretch it in one direction. Mark the point C where the mid-point lies. Now stretch the rope in the other side and do the same thing. You get two points C and D, and the line joining them is the perpendicular bisector.
