A device for providing a visual indication of data represented by magnetic polarity alignments at each of a plurality of disparate magnetized regions defining a fixed two-dimensional pattern. The device comprises a board containing a plurality of disks positioned in said fixed pattern, which disks are constrained to rotate with their flat surfaces in the plane of the fixed pattern. Each disk comprises magnetized magnetic material having a magnetic polarity alignment parallel to a given flat surface of the disk and a plurality of visible indicia positioned on the given flat surface of the disk in a predetermined order in relation to the polarity alignment. A mask is positioned on the board to cover the disks and contains apertures aligned over a predetermined portion of each disk position for providing a view of whichever ones of the visible indicia on the disks are rotatably aligned with the apertures.