Abstract: A coordinate input system to which control data (a displacement value), concerning the location and the posture of a displayed graphic object, can be input with a conventional coordinate pointing device, such as a mouse, and a method therefor. Coordinate values of three sequential input points P.sub.n, P.sub.n+1 and P.sub.n+2, which are entered with a coordinate pointing device, such as a mouse, are employed to calculate the central angle .angle.P.sub.n O.sub.n P.sub.n+2 relative to the arc P.sub.n P.sub.n+1 P.sub.n+2 of the circle O.sub.n circumscribed about these three points. Then, the angle .angle.P.sub.n O.sub.n P.sub.n+2 is employed to acquire the central angle .angle..theta..sub.n for the arc P.sub.n P.sub.n+1. A logic circuit or an upper-level program that waits for the input of the dial rotation value as control data employs the central angle .angle..theta..sub.n, which is acquired by inputting the coordinate values of the two sequential points P.sub.n and P.sub.