The last letter raises an obvious question - can’t several books fit on the Left, or Middle, or Right side of the shelf? However, I foresaw the need to re-adjust the location of books in the future.

A book used frequently today may not be needed in the future, as my research projects change. The book or books which replace it on the shelf would be unlikely to have the same number of pages. I realized that there would ultimately be no benefit to assigning a sequential number to each book on the shelf, since a single thick book with many pages might be replaced with two or more thinner books, and corrupt the system. I wanted the option of being able to keep selected current books which were used frequently on relatively low shelves, while moving less-frequently used books to higher shelves. I thus had to allow for flexibility in the location on the shelf.

By assigning books to a shelf range of approximately 8-10 inches, I could place two or three books from a given location and replace them with a different number of books from another location. In this way, the collection was always maintained for my current needs if I wanted to change it, or could be left alone if I didn’t want to rearrange books for a brief project.