"I believe that Johann Sebastian Bach notated a specific method of keyboard tuning. He did not express it in our normally-expected formats of theory, or numbers. Rather, he drew a diagram for a practical hands-on sequence to adjust the tuning pins, working entirely by ear.
He also demanded and exhibited a system of this enharmonic flexibility through the music in Das Wohltemperirte Clavier, presenting his tuning challenge (and giving the solution!) where most of the preludes and fugues each require the smooth handling of more than 12 notes. For example, his D major prelude and fugue use all of Bb, F, C, G, D, A, E, B, F#, C#, G#, D#, A#, and E# in the same piece: 14 notes. Some of the other pieces require 13, 15, 17, or 25!"
