Start with one unambiguous key
In C major, C is the chord on the first scale degree, F on the fourth, and G on the fifth. A common notation writes these as I, IV, and V. Lowercase numerals often indicate minor triads, so A minor is vi in this context. The numeral tells you a relationship to the tonal center rather than a fixed pitch. Establish the key first and keep the example simple. Without a clear reference, a numeral can look precise while describing an uncertain interpretation of the music.
Translate a short progression both ways
Take C, G, A minor, and F and write I, V, vi, IV. Then rebuild that relationship in G major as G, D, E minor, and C. Play both versions with the same rhythm and listen to the similar harmonic route. Preserve the chord quality as well as the root movement. This exercise is useful on guitar, piano, or ukulele because it connects physical shapes to a transferable idea. Use comfortable voicings so the ear can focus on the relationship rather than a difficult fingering challenge.
Map a six-bar phrase into another key
Use this original phrase in D major: D for one bar, Bm for one bar, G for one bar, A for one bar, Em for two beats, A for two beats, and D for the last bar. Its map is I–vi–IV–V–ii–V–I, with the fifth bar shared by ii and V. Count the D-major scale D, E, F sharp, G, A, B, C sharp to locate each root. Lowercase vi and ii preserve the minor qualities of Bm and Em.
Rebuild the phrase in A major: A, F sharp minor, D, E, B minor for two beats, E for two beats, then A. Test it by playing or singing the roots before adding full chords. If you accidentally use B major, the root degree is right but the quality is wrong. If every chord lasts a bar, the names are right but the phrase has gained a bar. A transferable map therefore includes durations as well as Roman numerals.
Leave room for chords outside the basic scale
Real songs can contain borrowed chords, altered tones, and key changes that need more careful notation. Do not replace an unexpected AudioChords label just because it does not fit the first simple numeral pattern you learned. Verify the sound, then seek an explanation appropriate to the context. Keep the original chord names alongside your numeral map while learning. Roman numerals are a tool for comparison and transposition, not a requirement to reduce every arrangement to four familiar functions. Their value is clearest when they help you recognize a relationship and play it accurately in another key.
Preserve inversions and durations
Keep slash bass notes separate from root degree. In D major, D/F sharp remains a tonic chord with its third in the bass; it does not become iii merely because F sharp is the lowest note. For a first notebook chart, writing I with D/F sharp beside it is clearer than using inversion figures you have not learned. Do not force a chromatic chord into the nearest scale chord to complete a tidy diagram. Leave its original symbol intact and investigate it later. AudioChords chart transposition can support this exercise, but the recording remains at its original pitch, so rehearse the new version without treating the unchanged audio as a matching backing track.