⌂ Drawing an accordion standard stradella bass system

Lilypond has amazing drawing capabilities. This example demonstrates how to draw a Stradella bass system as described here Stradella bass system.
The Buttons Ab , C and E are marked.
To mark a specific button by outlining it, enter its row and column number:
first number: column (0=Beses , 19=A#)
Second number: row (1=diminished chord, 2=7th chord, 3=minor chord, 4=major chord, 5=root note, 6=counter bass note)
If the parameters are outside this range no button is outlined.
Change the scale factor to a number you like.
Usage: \markup \scale #'(0.75 . 0.75) \accordion-bass #4 #2