Limits of the assumed ±7 km tolerance (see text) shown as horizontal green lines and the black dashed line is the best-fit ellipse. Upper panel: red points (R_D) are the distance of each point from the best-fit ellipse (in the normal-to-the-ellipse direction) as a function of the position angle, and the solid black line is the model with 1σ uncertainty represented in gray. Lower panel: residuals after subtracting the model from the data points.