A one centred arch also known as a Flat or Georgian Arch. It differs from all other arches in that the extrados is flat, to gauge with a course, while the intrados has a slight rise, or camber, to avoid the illusion of sagging. Therefore, the cutting angle of each voussoir varies and because of this it is usually built as a Gauged Arch. Geometrically set out as a horizontal band across the face of a circular arch with the intrados as the base of an inverted equilateral triangle whose apex gives the striking point.