Every circle has a center, a radius and a diameter twice as long. Wrapping string around a can shows the circumference is a little more than three diameters: C = πd = 2πr, with π used as 3.14. Cutting a circle into wedges and laying them as a near-rectangle shows the area is half the circumference times the radius, A = πr². The crew sizes the round window for the cardboard clubhouse at the Blueprint Table.