Returning to the exemplary CPO Ruler, it is now newly feasible to provide on a PCB not only an entire electronic circuit, but also pedagogical information about it such as its schematic diagram, parts identification data, performance data, multiple alternative informational labels for the circuit or its components, data for its use, opportunities for safe effective owner-builder modification and upgrade, and not inconsequentially, exposed direct viewing of the finished device or appliance that permits the builder's work to be a source of well-earned pride of accomplishment. In one embodiment, the visible surface of the CPO Ruler is marked with a table of data teaching the association of sounds in Morse code and their character or prosign equivalents.