Model A spark plug chart identification
 

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.

Re: Model A spark plug chart identification
 

It came from a MARC newsletter. Here is a link.
https://www.fordbarn.com/forum/showt...2931&showall=1

Re: Model A spark plug chart identification
 

It's signed by Ed Eaton and dated 1986. If memory serves, Ed Eaton was involved with the Judging Standards committee back on the 1980's. Perhaps someone else can shed more light on this??