Some of you may have already known about this but it's new to me.
I learned of this feature in a discussion on the Amazon boards which used a book called
"Basic Relativity" by Richard A. Mould. Some author/publishers have designed their books to show a larger versions of diagrams which don't always render well in e-ink.
You can download a sample and see for yourself (Locations 141-43, Figure 1.1).
For those without Kindles, I'm attaching some images.
zoom1 = the page as it looks at a level 3 size on my Kindle
zoom2 = when I scroll to the image and click, a "zoom" choice is available in the menu
zoom3 and zoom3a = a larger rotated image appears