MIDI Mapping info and a short rant on organ scales

Self-playing mechanical instruments were controlled by holes in paper or pins on a cylinder (like your wind-up music box), so each vertical column represented one note or action that the instrument would take.  The layout of these vertical columns is called a "scale."  

To save space and reduce size, most of these instruments would omit some notes, especially in the lower registers, and use those columns for something else.  Some carousel and band organs only had four bass pipes!  The arranger would compensate by transposing into a key that used those notes.  In the early days of converting from paper to MIDI, these columns were simply translated to MIDI notes, which resulted in MIDI mappings like the one my machine uses.