Going clockwise from C at the top, each key starts a fifth higher than the one before and adds one sharp: G has one, D two, A three, and so on. Going anticlockwise, each key starts a fifth lower and adds one flat: F has one, B♭ two, E♭ three. At the bottom the two sides meet, where F♯ and G♭ are the same key written two ways.
The outer ring holds the major keys, the inner ring their relative minors, which share the same signature. The small number at the edge is the number of sharps or flats.
A key and its family
When you select a key, its neighbours light up too. The key to its right is its dominant, the one to its left its subdominant, and the minor keys just inside are the relative minors of all three. Together they make up the six main chords of the key: in C major, that is C, F, G, Am, Dm and Em, exactly the chords the panel shows.
What it is good for
Finding the chords of a key quickly: the I, IV and V chords always sit side by side.
Writing progressions: moving anticlockwise, one step at a time, is the strongest chord movement in music (the basis of ii–V–I).
Changing key smoothly: keys next to each other differ by one note, so modulations between them barely jolt.
Reading key signatures: count the steps from C and you know how many sharps or flats to expect.
A way to remember it
The order of the sharps, F C G D A E B, is the order of the flats backwards. Many students learn the sharps with a short sentence whose words start with those letters. Make up your own: a sentence you invented yourself is the one you remember.
