the system effects positioning of an art work at precise given x and y rectangular coordinate points . this art work may correspond to drill hole positions in a printed circuit board . by recording in memory the exact rectangular coordinate points on the art work and the necessary servo signals to effect exact centering at the coordinate points , accurate circuit board drilling can be carried out . a circular hole is provided in the art work and an image of this hole projected to a screen having horizontal and vertical cross hairs defining x and y axes respectively . the art work is precisely positioned at a given pair of rectangular coordinates when the intersection of the cross hairs corresponds exactly with the exact center of the image of the circular hole . exact centering is achieved by causing first and second light responsive photo cells to oscillate along the x and y axes directions respectively , the centers of oscillation of the cells corresponding to the intersection point of the cross hairs . if the projected image of the hole is off center , a cell or cells will be exposed to light longer on one side of its center position than on the other . stated differently , the projected image will only be centered when the scanning cells are exposed to light for equal time intervals on either side of their center of oscillation positions . the difference in such time intervals is used to generate a corrective signal for operating the servos to effect precise center positioning .