Protractor on the dial from 180°, as the dial is graduated from opposite zero marks to 90° each way. Since the spaces, both on the main scale and the Vernier scale, are numbered both to the right and to the left from zero, any angle can be measured. The readings can be taken either to the right or to the left, according to the direction in which the zero on the main scale is moved. Reading the Vernier scale: The bevel protractor Vernier scale may have graduations of 5′ (minutes) or 1/12°. Each space on the Vernier scale is 5′ less
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