If we look at the whole Book at once, we can see that the book is divided in two parts. The first part is the longer one and consists of written text, while the second part is filled with a few pages of drawings and plans.
The first pair I chose consists a chapter change. The Text is arranged in one block. There isn’t space between the chapter III. an IV. In my opinion very unusual to beginn a new chapter on the same page.
The second pair of pages I chose, is an illustration on the right side and an empty one on the left, I guess for some notes or drawings.
If we compare it with the last pair, we can see the different ways to label an illustration.