Mathematically, a right angle is defined as 90°. It represents a quarter of the full angle, which is 360°. The right angle occurs in many geometric figures and constructions and is indicated in drawings by a small quarter circle with a point or a small square. Straight lines, lines, surfaces, or solids that intersect or touch at right angles are called right-angled, perpendicular, or orthogonal. According to the specifications of the DIN and ISO standards on form and position tolerances, perpendicularity is also a type of direction tolerance, i.e. a position tolerance. The perpendicularity of a surface is tolerated if the surface lies between two planes that are orthogonal to the reference. For axes, perpendicularity tolerance is considered to exist if the toleranced cylinder axis lies in a cylinder that is perpendicular to the reference surface. Rectangular structures are well suited to support perpendicular compressive loads. For marking two structural elements that are guaranteed to be perpendicular to each other, there is a square with an integrated inverted T as a standardized symbol.