Protractor Protractor A protractor is a measuring instrument, typically made of transparent plastic or glass, for measuring angles. Most protractors measure angles in degrees (°). Radian-scale protractors measure angles in radians. Most protractors are divided into 180 equal parts. Some precision protractors further divide degrees into arcminutes. They are used for a variety of mechanical and engineering-related applications. One common use is in geometry lessons in schools. Some protractors are simple half-discs. More advanced protractors, such as the bevel protractor, have one or two swinging arms, which can be used to help measure the angle. A bevel protractor is a graduated
Circular chess advance only opens one square for the bishop. Some players advance the central pawns first anyway, while others prefer to advance the rooks' pawns in order to open lines of attack for the more powerful pieces; it is not known which move, if any, is objectively best. The different geometry of the square and circular boards creates considerable differences in endgame theory: three of the four "basic checkmates" on a square board (those with king and rook, king and two bishops, or king and bishop and knight against a lone king) rely on forcing the defending king into the corner