CPO Ruler acoustic output can be achieved using an oscillator circuit such as a multivibrator circuit. In one embodiment, the multivibrator circuit output is buffered and provided to the user via an SMD audio jack. In a preferred embodiment, the resistance values between the buffer amplifier and the audio jack are selected and optimized to permit either monophonic or stereophonic load attachment and either earbud or headphones for individual listening or attachment of an active speaker for group or classroom use. In a preferred embodiment the CPO circuit comprises a SMD coin cell-type battery to provide electrical power without the necessity to attach an external battery to power the CPO.

In one embodiment, the circuit schematic of the CPO oscillator circuit is printed visibly on the Active Ruler to assist in pedagogy, construction, diagnosis, repair, and maintenance of the Active Ruler. In one embodiment, the formula for determining or estimating pitch frequency of the CPO oscillator is printed on the visible surface of the CPO Ruler, thereby providing the builder with directly accessible data required to adapt the CPO Ruler through use of alternative SMD components for pedagogical purposes or personal preference. In one embodiment, pedagogical information such as schematic depictions of certain important or hard-to-remember data, such as the distinction between a PNP and NPN bipolar transistor, are visibly present on the surface of the Active Ruler to assist in pedagogy, construction, maintenance, repair, and upgrade of the Active Ruler. In one embodiment, useful formulas are printed on the Active Ruler visible surface, beneficially supporting pedagogy and available for later use for reference purposes. Additional tabular or reference data are printed on either side of the Active Ruler to enhance its utility as a pedagogical and reference tool.