This ZX Spectrum accessory is neither hardware nor software, but is a book of gridded tracing paper, which claims to help convert your "illustrations, maps, charts, photos etc” into a set of pixel locations on your 256×192 screen. Designed to be used by programmers/artists to help design computer graphics.
PDFs of gridded A4 size paper to help convert your "illustrations, maps, charts, photos etc” into a set of pixel locations on your 256×192 screen