Providing that the style, or shadow-casting edge, of a sundial is parallel to the Earth's axis, hour lines can be drawn on any surface on which the sun shines. This allows the designer of dials to make them in a great variety of shapes, with plane or concave faces. One of the simplest forms is the cube, with dials on the top and four vertical sides. Another is the octagon with vertical sides, with or without corresponding sloping sides above or below the vertical ones. The whole may be capped by a horizontal dial, or by a decorative finial. One form of the polyhedral dial is the crucifix, a cross hinged to a base with the time shown by the shadow of an edge of the cross on a neighbouring face.