Progressions in C# — Cello

C# major harmonises to C# – D#m – Fm – F# – G# – A#m – C°; C# minor to C#m – D#° – E – F#m – G#m – A – B. Each chord links to its tone map on the Cello, so a tune in C# becomes a short list of places the hand needs to be.

The useful question in a key is which open strings it agrees with. In C#, check the chords against the open C and A — a key that leaves an open string ringing under the melody is a key this instrument was built for.