Unit of circular measure. Measure off on the circumference of a circle a length equal to the radius. The angle at the centre of the triangle so formed = 1 radian = 57. 3°; 1° = 0. 017 radian; π(3. 14…) radians = 180°
H. J. Porter (Chairman - Technical Committee), Dictionary of Fire Technology, The Institution of Fire Engineers, The Victory Press (Leicester) Ltd. 1979 UK. (Fr Tech - Brit) {81}