"2001.09.10" . "ANGLE" . "ANGLE" . . "Qualified" . "u82237" . "PLANE ANGLE" . "RDS358019" . "ISO 31-1:1992(E)" . "An angle between two half-lines terminating at the same point is defined as the ratio of length of the included arc of the circle (with its centre at that point) to the radius of that circle" .