Model A spark plug chart identification

[guam2250]

Evening all. Can anyone ID this Model A spark plug chart? It has a#17 at the bottom corner, so it was part of a book? Some of the info is in conflict with judging standards, such as the "3" in the 3X plugs has a flat top, not rounded. There is a 3X , dated 1-29 to 11-30, with the knurling different than the standards. Curious where this came from and accuracy issues.