On a guitar, a capo is one action. On a five-string banjo it is two, because the short fifth string does not reach the nut: its own nut sits at fret 5, so a neck capo passes underneath it entirely and the drone has to be raised separately at a spike or a sliding fifth-string capo.
That one physical fact is the only thing this section declares. The registry records the drone's pitch but not where its nut is, so the fifth string's nut is at fret 5 is stated once, in the engine, with a comment saying so — and every number on every page below is arithmetic over it.
The whole table, derived
| Neck capo | Key | Spike fret | Drone sounds | Pitch |
|---|---|---|---|---|
| Fret 1 | G# | 6 | G# | 68 |
| Fret 2 | A | 7 | A | 69 |
| Fret 3 | A# | 8 | A# | 70 |
| Fret 4 | B | 9 | B | 71 |
| Fret 5 | C | 10 | C | 72 |
Why the spike is five frets further
Because the drone starts five frets late. Raising the neck strings by n semitones means fretting them n frets up from their nut at fret 0; raising the drone by the same n means fretting it n frets up from its nut at fret 5. Hence n + 5, every time, and the drone's pitch is simply its open pitch plus n. CI recomputes both halves independently and fails if they disagree.
Capo or retune?
A capo moves the key and leaves the instrument's logic intact — every shape, every roll, every scale map still applies with a new name. A retune changes what the open strings are, which is a different instrument with a different set of easy chords. Choose the capo when you want the same music in a new key, and the retune when you want different music.