Abstract: A sheet-like pad having a grid pattern constituted by X-axis grid lines and Y-axis grid lines perpendicular to the X-axis grid lines, and adapted to be placed between a document and an optical reader of a type which comprises an optical scanner for scanning the document to read an image on the document while the document is radiated with first rays of light emitted therefrom and a position sensor for reading the grid pattern for locating the position of the optical reader on the document while the document is radiated with second rays of light emitted therefrom. The sheet-like pad comprises a film-like base having upper and lower surfaces opposite to each other, reflective layers formed on the upper surface of the base for periodically reflecting the second rays of light in first and second directions perpendicular to each other, and a protective layer formed on the upper surface of the base so as to overlay the reflective layers.