Hi Richard,
A. The book with the Model A Ford Service Bulletins, February 1929, (Ford's page 318), gives an excellent description of the two (2) tooth "Adjustment Steps" to be "sequentially" followed in the exact order given.
B. The small diagram, Figure 644 on page 320 was later made larger & reprinted on the same book's page 363, Figure 740, in the Ford's July 1929 Bulletin.
C. Unless one has a magnifying glass, it would be an excellent idea to even enlarge the book's Figure 740 diagram because:
(1) Of "utmost" importance is to study the notes in each of the four (4) separate diagrams; and,
(2) Secondly of even "more" importance is to study four (4) different diagrams indicating four (4) "different" locations of the indicated "center" of the two (2) tooth sector shaft, (Ford's part #A-3575C), which is also emphasized with X & Y coordinate crosshairs.
D. The "correct" location & correct "sequential" adjustment of the "center" of this sector shaft, (shown in the bottom right diagram) is the key to make the steering function 100% correctly.
E. In addition, if one wants, one should also read Mr. Les Andrews' adjustment procedure which closely follows the 1929 Ford steering adjustment procedure.