Abstract: Particular zones are given a distinctive appearance with respect to surrounding areas on a surface such as a printed-circuit board to be drilled in an automatic process. The surface is automatically scanned in a system of two rectilinear perpendicular coordinates by a reader comprising at least one detector which is responsive to the distinctive appearance. The coordinates of the surface points for which the detector delivers a signal representing the presence of the distinctive appearance during the scanning are recorded in a coded form which can be utilized by the automatic machine.