1 Gradian:1 gradian is exactly 1/400 of a revolution or 2π/400 or 0.9°. In terms of the SI unit radians 1 grad is approximately 15.707 963 x 10-3 rad.
Circle:A circle is a simple closed shape. It is the set of all points in a plane that are at a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves so that its distance from a given point is constant. The distance between any of the points and the centre is called the radius.