The circle of fifths is a remarkably useful diagram for the analysis of music. It shows the twelve notes of the chromatic scale arranged in a circle, with notes that are harmonically related (like C and G) being close together and notes that are discordant (like C and C♯) more distant from each other.
The Tonnetz diagram (note that the arrangement here is inverted relative to that used in the text. It appears that there is no rigid standard, and several arrangements are in use) [Image from WikimediaCommons].
where 
is the radius. Some of us may also remember that the volume of a ball — the interior of a sphere — is 
.
ThatsMaths 