I created this chart many years ago after I had purchased an accordion at a yard sale. After a bit of tinkering, I realized that the bass (buttons) side of a piano accordion is cleverly arranged in a “circle of fifths” approach to make it very easy to find the 4 chord and the 5 chord adjacent to the 1 chord in whatever key you might be playing. I arranged this chart in the same way:
The chart is organized in rows according the key. So for instance, if you find the row marked “D”. All the chords in that row are “D” chords organized in columns such as Major, Minor, Seventh, and so on. If you look at the row above the “D” row, you’ll see that it’s the “G” row. That is the “4” chord of the key of “D”. The row below the “D” row is “A” which is the “5” chord of the key of “D”. This chart then helps not only to show you the guitar chords, but also helps you identify the 1-4-5 chords of each key. Most rock songs essentially use the 1-4-5 chords to create the song form.
The numbers 1-4-5 and so on should not be confusing if you simply think of the scale. For instance the D scale is D, E, F#, G, A, B, C#, D. If you simply add numbers to each of these notes, you’ll see that D=1, G=4, A=5.