จากกระทู้ของน้า กีต้าร์เก่าครับ

[napman]

It's just another image of "Circle of 5th"

http://www.google.com/search?q=circle+of...h=961&prmd

From "Wikipedia"

Definition

Since the term 'fifth' defines an interval or mathematical ratio which is the closest and most consonant non-octave interval, then the circle of fifths is a circle of closely related pitches or key tonalities. Musicians and composers use the circle of fifths to understand and describe those relationships. The circle's design is helpful in composing and harmonizing melodies, building chords, and moving to different keys within a composition.[1]

At the top of the circle, the key of C Major has no sharps or flats. Starting from there and going clockwise by ascending fifths, the key of G has one sharp, the key of D has 2 sharps, and so on. Similarly, going counterclockwise from the top by descending fifths, the key of F has one flat, the key of B? has 2 flats, and so on. At the bottom of the circle, the sharp and flat keys overlap, showing pairs of enharmonic key signatures.

Starting at any pitch, ascending by the interval of an equal tempered fifth, one passes all twelve tones clockwise, to return to the beginning pitch class. To pass the twelve tones counterclockwise, it is necessary to ascend by perfect fourths, rather than fifths. (To the ear, the sequence of fourths gives an impression of settling, or resolution. (see cadence))