Major scale
The numbers inside the circle show the number of sharps or flats in the key signature, with the sharp keys going clockwise, and the flat keys counterclockwise from C major (which has no sharps or flats.) The circle depends on enharmonic relationships in the circle, which is six sharps or flats for the major keys of F = G and D = E for minor keys (Drabkin 2001). Seven sharps or flats make major keys (C major and C major) that are more easy to spell with five flats or sharps (as D major or B  major).