Use Arc/Centre,R,Start,End to create an arc by centre, radius, start angle, and end angle. Specify CW or CCW direction.
Use Arc/Centre,R,Start,End. Specify the centre point, radius, start angle, end angle, and sweep direction (CW or CCW). Angles are measured from the positive X axis, counterclockwise. 0=rightmost, 90=top, 180=leftmost, 270=bottom.