An L-shaped diagnostic tool is preferably made from paper with a backing having a contact adhesive. Each arm has a ruler, with origins co-aligned at the internal corner of the intersection of the arms. One arm has representative color images of afflictions for each of the various ranks within a classification system. The other arm contains textual descriptions of the salient features of afflictions in each rank. A photograph of the L-shaped tool placed around the affliction may be taken for diagnostic and monitoring purposes.