The proportional compass, is the earliest and simplest version of reducing and enlarging instruments. They have two pointed arms like dividers, and operate line by line. The more complex and much larger pantograph was invented about 1603 by Christoph Scheiner. It is a large drawing apparatus typically about a meter long with four pivoting arms. The arms are hinged and articulated such that one pen draws a larger version of the other. The ediograph is an 1821 improvement over the pantograph that incorporates three arms with cables and pulleys. The protractor is a flat circular arc graduated in 360-degree marks or more commonly a semi-circular arc graduated in 180° that is used to measure and draw angles. Square sets are usually flat straight edged triangles with one right angle in combination with either two 45° angles or 30° and 60° angles.