Is anyone familiar with some freely available guide explaining in detail how to read Bach's organ tablature notation?
Apparently, Bach was very comfortable in using the tablature notation, especially in his youth, probably because it saved him a lot of time when copying music, not to mention the paper, due to its compactness. Supposedly, the great Passacaglia in C minor, BWV 582 was originally written this way.
Here is a great example of the notation, Fantasia in C minor, BWV 1121:
Now, I can compare this to the sheet music version (which is available on IMSLP, for example) and I can figure out some patterns (it's very similar to our modern abc notation, for example), but without some guide on the symbols, and considering the fact Bach's handwriting is at places unclear, it makes it very difficult to figure it out.