Fig 11. Spindle torus showing location of a toric lens surface KLMN on torus. XX" is axis of revolution of torus. Circle AZB is equator of spindle lotus, and PZP" is a principal meridian. YY", normal to the surface at Z, is axis of toric lens surface whose equatorial principal curve LZN has a greater curvature than meridional principal curve KZM. Note that YY" is perpendicular to XX" at point O, which is geometric center of spindle torus.