This is a recommendation for future versions of the document, namely, revision of a diagram to improve accuracy and reduce potential confusion.

It seems clear that the oven walls are 4.5" thick, as per p.30, section "About Your Brick", paragraph 2 and p.33, section "Subsequent Courses", paragraph 1 (these refs pertain to version 1.2 of the document).

However, in the "Cross Section: Igloo" diagram on p.14, the oven dome is clearly not 4" thick relative to the other measurements shown in the same diagram, it is 2.5" thick in that diagram as a matter of fact, same as the cooking floor.

I'm just suggesting fixing that diagram. That's all.