A chart for finding chords on the guitar or other string instruments.
Here is an example of the chart for major chords on the guitar:
C B Bb A Ab G Gb F E Eb D Db
E 3|--|--| 5|--|--|--|--| 1|--|--|--| 3|--|--| 5|--|--|--|--| 1|--|--|--|
B --| 1|--|--|--| 3|--|--| 5|--|--|--|--| 1|--|--|--| 3|--|--| 5|--|--|--|
G 5|--|--|--|--| 1|--|--|--| 3|--|--| 5|--|--|--|--| 1|--|--|--| 3|--|--|
D --|--| 3|--|--| 5|--|--|--|--| 1|--|--|--| 3|--|--| 5|--|--|--|--| 1|--|
A --|--|--| 1|--|--|--| 3|--|--| 5|--|--|--|--| 1|--|--|--| 3|--|--| 5|--|
E 3|--|--| 5|--|--|--|--| 1|--|--|--| 3|--|--| 5|--|--|--|--| 1|--|--|--|
Say you want to find a G major chord. First you find G in the top row. The vertical line below G represents the nut, each vertical line to the right represents a fret, and each line to the left can be ignored. Then each 1 represents where to put your finger to play the root of the chord, each 3 represents the major third, and each 5 represents the perfect fifth. In this case each 1 is a G, each 3 is a B, and each 5 is a D. This makes it quick to find all the possible ways to play a G major on the guitar, and you can see what inversions are possible. See if you can find some familiar chord shapes in this chart.
The createChart function will automatically generate such a chart for any chord as described as a list of intervals in semitones, e.g. a major seventh chord is [0, 4, 7, 11]. You can also specify a different tuning, so this generalizes easily to any string instrument. Several chords and tunings are preprogrammed in.
I invented this when I was learning guitar and it helped me a lot. It helped in the early stages when I was learning basic chords, and was still helpful in the later stages when I was learning jazz. Hopefully this can help you understand your instrument better too.