Join two corresponding points of the image and the object and draw perpendicular bisectors for each of them the point of intersection of the two perpendicular bisectors is the center of rotation ...further join one of the pointsof the image like S to the centre of the graph and join the S’ also tho the centre and measure the angle that connects both S and S’ to the centre...So the description you will mention the angle of rotation as well as the center of rotation
