The height hn of the center of the nth circle above the base diameter ACB equals n times dn.[1] This may be shown by inverting in a circle centered on the tangent point A. The circle of inversion is chosen to intersect the nth circle perpendicularly, so that the nth circle is transformed into itself. The two arbelos circles, CU and CV, are transformed into parallel lines tangent to and sandwiching the nth circle; hence, the other circles of the Pappus chain are transformed into similarly sandwiched circles of the same diameter. The initial circle C0 and the final circle Cn each contribute ½dn to the height hn, whereas the circles C1–Cn−1 each contribute dn. Adding these contributions together yields the equation hn = n dn.