this way, by applying a sundial to every surface of a solid object. In some cases, the sundials are formed as hollows in a solid object, e.g., a cylindrical hollow aligned with the Earth's rotational axis (in which the edges play the role of styles) or a spherical hollow in the ancient tradition of the hemisphaerium or the antiboreum. (See the History section above.) In some cases, these multiface dials are small enough to sit on a desk, whereas in others, they are large stone monuments. A Polyhedral's dial faces can be designed to give the time for different time-zones simultaneously. Examples include the Scottish sundial of the 17th and 18th century, which was often an extremely complex shape of polyhedral, and even convex, faces. Prismatic dials Prismatic dials are a special case of polar dials, in which the sharp edges of a prism of a concave polygon serve as the styles and the sides of the prism receive the shadow. Examples include a three-dimensional cross or star of David on gravestones. Unusual sundials Benoy dial The Benoy dial was invented by Walter Gordon Benoy of Collingham, Nottinghamshire, England. Whereas a gnomon casts a sheet of shadow, his invention creates an equivalent sheet of light by allowing the Sun's rays through a thin slit, reflecting them from a long, slim mirror (usually half-cylindrical), or focusing them through a cylindrical lens. Examples of Benoy dials can be found in the United Kingdom at: Carnfunnock Country Park, Antrim Northern Ireland Upton Hall, British Horological Institute, Newark-on-Trent, Nottinghamshire Within the collections of St Edmundsbury Heritage Service, Bury St Edmunds Longleat, Wiltshire Jodrell Bank Science Centre Birmingham Botanical Gardens Science Museum, London (inventory number 1975-318) Bifilar sundial Invented by the German mathematician Hugo Michnik in 1922, the bifilar sundial has two non-intersecting threads parallel to the dial. Usually the second thread is orthogonal to the first. The intersection of the two threads' shadows gives the local solar time. Digital sundial A digital sundial indicates the current time with numerals formed by the sunlight striking it. Sundials of this type are installed in the Deutsches Museum in Munich and in the Sundial Park in Genk (Belgium), and a small version is available commercially. There is a patent for this type of sundial. Globe dial The globe dial is a sphere aligned with the Earth's rotational axis, and equipped with a spherical vane. Similar to sundials