Harmony Calipers is a visual songwriting companion for musicians. Use the Circle of Fifths as a harmonic map to explore chord relationships, build progressions, arrange song sections, and export clean chord charts or PDF song packs. Harmony Calipers is designed for musicians working with a real instrument nearby. Sit at a piano, hold a guitar, mandolin, ukulele, banjo, or another chordal instrument, and use the app to organize harmonic ideas into playable song forms. What you can do with Harmony Calipers: Explore chord relationships Use the harmony wheel to see how chords relate across the Circle of Fifths. Select tonal centers, compare harmonic distance, and view relationship paths directly on the wheel. Browse suggested progressions Start from suggested chord progressions organized by musical function, mood, and relationship type. Color badges help identify functional harmony, stable diatonic movement, dominant tension, caliper-derived ideas, and progressions that may need review. Customize progressions Send any suggested progression into the Custom Progression builder. Edit the title, chord sequence, tonal center, mode, and harmony type, then validate the result. Build songs by section Use Song Builder to arrange progressions into song forms. Add sections such as Intro, Verse, Chorus, Bridge, Break, Interlude, and Outro. Reorder sections to shape the structure of the song. View chord charts Harmony Calipers includes piano chord charts and fretted instrument charts for guitar, mandolin, mandola, ukulele, baritone ukulele, and banjo. Export your work Export full song charts, individual section sheets, traditional chord chart layouts, modern Harmony Calipers layouts, and PDF song packs. Designed for visual writing Harmony Calipers does not try to replace your instrument. It helps you see harmonic relationships, organize chord ideas, and create usable charts so you can play, revise, and develop songs with your own instrument. Good for: - Songwriters building chord progressions - Composers - Bands that want to ensure every player has the same information - Guitarists, pianists, and multi-instrumentalists - Music theory learners - Teachers creating chord examples - Players exploring the Circle of Fifths - Musicians who want clean printable chord charts Harmony Calipers turns harmonic ideas into organized song forms.