A method for mapping a point outside a halftone cell to a point inside the halftone cell by determining the size of a rectangle which is tiled exactly by the halftone cell. Information related to available topics is classified by type, and at least two types of information related to the designated topic andor type are provided to the user. as shown in the Examples, and thus its industrial value is significant. The sensors are oriented relative to the conveyor so that packages passing over the sensors are detected by the sensors and produce a signal correlated to said package size.