Protractor for measuring or constructing angle, has outer and inner graduations of different color, segments comprising colors same as that of respective graduations and other segments perpendicular to graduated bicolor rule

摘要

The protractor has outer and inner graduations (1, 2) of different color, a segment (3) originating from protractor center (8) and arriving to zero of the graduation (1) and a segment (4) originating from the center and arriving to zero of the graduation (2). The segments (3, 4) have colors same as that of the graduations (1, 2), respectively. A segment (7) leaving from the center to zero of graduated bicolor rule is extended by a segment (9), where the segments (7, 9) are perpendicular to the rule.