Online Chord Clock

You can even use the Chord Clock right on your Computer.

This Chord Clock Face shows the 10 most common chords in 12 different keys. if you put your cursor on one Group and point to another group with a finger, the chords in the Fingergroup are in the same relationship to each other as the chords in the Cursor  group.

Example:  You have a song you found in a book or on the internet with a lot of F, C, Bb chords, maybe some Dm chords. Looking at the diagram chord groups, key of F (on right side) has those chords in it, in fact they are top row and second row chords. Song is most likely in Key of F. 

Put your Cursor on the F group. Now point with your Finger to the D group on top. See how D is in the same relative position as F is? And  G in the D group is in the same position as the Bb in the F group?

We can "transpose" the Key of F chords (F, C, Bb, Dm) to Key of D chords by comparing positions, and come up with D, A, G, Bm

F = D
C = A
Bb = G
Dm = Bm

So you can play the song by using D where song said F, and Bm where song said Dm, etc. Transposing means changing the chords in one key to the equivalent ( same relationship) chords in another key.

This is like how the Free Chord Clock works, it has moveable pointers instead of Finger and Cursor, but it works exactly the same way.