The diagram shows the evolution of stone tools over 600 thousand years.
Overall, it is clear that while the later example, which dates back to 0.8 million years ago, retained some features of its predecessor, which is believed to have been conceived 1.4 million years ago, it had become significantly more refined over time in terms of angularity and functionality.
The first specimen, Tool A, is relatively flat when viewed from its side profile. An immediately noticeable attribute is that the front and the back do not match, with the latter having a markedly smaller surface area than the former. The shape of the tool is not defined, though there is a clear pointier end and a wider end. In terms of the surface, Tool A is still quite rough and uneven.
Tool B is considerably more advanced than Tool A. It is still flat, but the shapes of the front and back align much better than they used to in the past. It has a more clearly defined teardrop shape, with a fat base that tapers aggressively towards a pointed tip. Tool B’s surface is also much smoother than Tool A’s, and the edge on the side is clearly sharper.