Originally Posted by sirbruce
Sextant. It's actually a picture of 17th-century Polish astronomers Johannes and Elisabetha Hevelius.
The numeric markings would indicate it's a sextant, but mapping it with rotation shows it to be short of 60° of arc, which was why I judged it to be an octant when eyeballing the angle. It is, however, wider than 45°; I suspect Amazon compressed the image some in width to get it to fit the 3x4 aspect ratio of the Kindle display.